1. Abstraction: a theoretical idea; also, the process of abstracting, the condition of being disassociated, an abstract work of art, or the quality of being preoccupied
2. Apprehension: the act or quality of becoming aware or grasping a meaning; also, the act of arresting someone or to a sense of foreboding
3. Assumption: a statement taken for granted; also, the act of taking for granted that something is true, or taking something on or laying claim to it, or arrogance or pretension
4. Belief: something held to be true or proper; also, a conviction that something is true, or the state of mind in which someone places confidence in someone or something
5. Brain wave: see brainstorm; also, variations in voltage in the brain, and resulting electrical currents
6. Brainchild: an idea or product one has thought up or created
7. Brainstorm: A sudden idea; also, a brief bout of insanity
8. Caprice: a sudden change in an idea or way of thinking; also, a whimsical inclination, or a lively musical composition
9. Chimera: a fantasy or unrealistic idea; also, an imaginary or mythological creature with anatomical features of various animals or biological phenomena involving genetic diversity in a single organism
10. Cogitation: a distinct idea; also, the act of thinking, or the capacity to do so
11. Cognition: the result of a mental process; also, the mental process itself
12. Conceit: an imaginative idea, or an idea held to be true or appropriate; also, excessive self-regard, a complicated or far-reaching metaphor, a theme, or a fancy trinket
13. Conception: an idea, or the result of abstract thinking; also, the forming or understanding of ideas, the body of ideas that constitute one’s understanding of something, or a beginning or the process of beginning pregnancy
14. Conclusion: an idea formed based on consideration, or a judgment or inference; also, a result or the act of bringing something to an end, or of deciding or summing up a legal case
15. Conjecture: an idea inferred or supposed, or reached by deduction; also, something that has yet to be proven or disproven
16. Conviction: a strongly held idea; also, the state of mind of someone who firmly holds an idea as true, or the act of finding someone guilty of a crime or the state of being found or having been found guilty
17. Delusion: an idea that is mistaken or misleading; also, the act of state of having false ideas, or holding such a false idea as a symptom of mental illness
18. Fancy: see primary definition of whim; also, liking for something, or imagination
19. Freak: see primary definition of whim; also, a strange event, person, or thing, or a person who is enthusiastic about or obsessed with something
20. Guess: an idea one has based on initial or incomplete information
21. Hallucination: an idea or sensory phenomenon produced by a drug or a mental disorder
22. Hunch: see intuition; also, a bulge or lump
23. Hypothesis: an unproven idea assumed to be true as a basis for experimentation or investigation
24. Illusion: see the primary definition of delusion; also, a misleading phenomenon, or the fact or state of being misled
25. Image: a mental picture, or an idea one is able to envision based on words; also, a depiction or picture, the ideal depiction of someone or something based on propaganda or publicity, or someone who closely resembles another
26. Impression: an uncertain or vague idea; also, the act of pressing something into a medium or material to make an outline of it, or producing a figurative equivalent in someone’s mind, or the literal or figurative result of such an action, or an imitation, for the purposes of entertainment, of a well-known person
27. Inspiration: an imaginative idea or feeling; also, something that prompts or is the product of such an idea or feeling, the quality or state of this condition, or the prompting of emotion or thinking, or the act of breathing in
28. Intellection: the act of thinking or reasoning
29. Intuition: an idea based on a sudden realization, or on feeling without conscious thinking
30. Kink: see the primary definition of whim; also, an unusual or clever approach, an eccentricity or fetish, a curl, twist, or other imperfection, or a cramp
31. Mind’s eye: the ability to envision ideas or depictions, or the product of this ability
32. Notion: an idea or understanding that may be imaginative or speculative; also, something believed to be true or appropriate, or, in plural form, practical personal or hygienic items
33. Observation: an idea based on awareness or notice; also, adherence to a custom, principle, or rule, the act of seeing or thinking about something or the ability to do so, the gathering of information or evidence, or the state of being noticed or watched
34. Opinion: a statement or idea one holds to be true or appropriate; also, a judicial statement summarizing a decision about a case
35. Perception: an idea based on noticing; also, awareness, or the ability to understand
36. Phantasm: a misleading idea; also, a fantasy, a ghost, or an illusion
37. Picture: a mental image; also, a copy, depiction, or image, an exemplar, or a set of circumstances
38. Preconception: an idea assumed before careful consideration
39. Prejudice: an idea or feeling of dislike or animosity about someone or something; also, wrong done to someone
40. Premonition: an idea or feeling of impending action or occurrence
41. Prepossession: see the primary definition of prejudice; also, an obsession with one idea or thing
42. Presentiment: see premonition
43. Reflection: an idea formed, or a comment made, after careful thinking; also, the act of careful thinking, or something that causes a negative response, or the return of light or sound waves from a surface, the creation of such a phenomenon, or the phenomenon itself
44. Speculation: consideration of what may be true or what may happen; also, a risky investment with potential for great profit, or the act of investing in this manner
45. Supposition: an idea based on preliminary consideration, or one that someone believes
46. Surmise: see guess
47. Theory: an unproven idea, or one presented for consideration; also, a group of ideas or principles
48. Thought: an idea formed in one’s mind; also, the act of thinking, a way of thinking, or an intention, or consideration or the power to consider
49. Vagary: an odd or unpredictable idea
50. Whim: an unusual and perhaps sudden idea; also, a rotating drum or shaft

1. Abstract: disassociation from a practical reference that would aid in comprehension
2. Abstruse: difficult because of technical considerations
3. Arduous: great physical exertion
4. Augean: unpleasantly, overwhelmingly hard (a classical reference to the Augean stables, cleaned by Hercules as one of his legendary twelve labors)
5. Backbreaking: tiring and often dispiriting physical effort
6. Bruising: physically wearing and damaging
7. Brutal: unpleasantly difficult
8. Burdensome: physically or emotionally difficult
9. Challenging: requiring special effort; may have a positive or a negative sense depending on context
10. Complex: difficult because of multiple interrelated factors
11. Complicated: see complex
12. Convoluted: see complex; with an additional connotation of twisting or intertwining
13. Cruel: marked by uncompromising difficulty that disregards the worker’s welfare
14. Daunting: inspiring a feeling of great difficulty
15. Demanding: suggestive of a great commitment of time and effort
16. Distressing: causing emotional anguish
17. Effortful: requiring effort
18. Elusive: difficult to comprehend, or evasive
19. Exacting: requiring meticulous attention to detail, or requiring relentless effort
20. Exhausting: difficult in terms of physical or mental exertion
21. Formidable: discouraging because of expected difficulty; also has a positive connotation of impressiveness
22. Frustrating: producing feelings of hopelessness or defeat
23. Grievous: causing pain or suffering
24. Grim: evidencing unyielding difficulty or severity; can also mean “grim,” “gloomy,” or “sinister”
25. Grueling (also spelled gruelling): requiring unrelenting or extreme effort
26. Hairy: difficult (informal)
27. Harsh: excessively difficult
28. Heavy: involving great effort
29. Herculean: suggestive of great difficulty
30. Inhuman: so difficult as to seem beyond human capability
31. Insoluble: seemingly too difficult to be solved or resolved
32. Intimidating: so difficult that the task or prospect inspires fear or hopelessness
33. Intricate: see complex
34. Involved: see convoluted
35. Knotty: see convoluted
36. Labored: requiring wearying physical or mental exertion
37. Laborious: see labored
38. Merciless: marked by effort that seems to be required with no regard for the welfare of the worker
39. Moiling: requiring much effort
40. Murderous: suggestive of risk of physical or mental harm (informal)
41. Onerous: see burdensome
42. Opaque: difficult because of a lack of clarity or communication
43. Oppressive: harshly difficult
44. Overwhelming: too hard to do or bear without suffering
45. Painful: causing physical or mental discomfort or harm
46. Pick-and-shovel: suggestive of great manual effort
47-48. Problematic/problematical: difficulty in solving a problem
49. Punishing: difficulty heedless of consequences of physical or mental strain
50. Recondite: difficult to comprehend because of obscurity or the need to possess more knowledge
51. Rigid: inflexibly difficult
52. Rigorous: difficulty caused by conditions of inflexibility or requirements of great precision
53. Rugged: suggestive of conditions requiring strength and stamina
54. Serious: requiring a great deal of effort
55. Severe: difficult because of the nature of requirements or constraints or because of the need to expend great effort
56. Spiny: replete with difficulties
57. Sisyphean: suggestive of relentless, repetitive toil (a classical reference to Sisyphus, tormented in Hades by having to repeatedly roll a boulder up a hill, then retrieve it when it rolls down again)
58. Stiff: see rigid
59. Strenuous: see arduous
60. Stressful: so difficult as to cause tension or nervousness
61. Strict: difficult especially because of standards imposed
62. Stringent: see strict
63. Stubborn: persistently difficult
64. Sweaty: suggestive of great physical exertion, causing perspiration
65. Tall: see formidable (informal)
66. Taxing: see burdensome
67. Testing: calling for great effort, as if to test one’s abilities
68. Thorny: see spiny
69. Ticklish: difficult because of the problem’s sensitive nature
70. Tight: hard because of a lack of flexibility
71. Toilsome: see labored
72. Tough: physically or mentally demanding (informal)
73. Tricky: see ticklish
74. Trying: requiring great endurance
75. Uphill: see labored

1. Ahold/a hold: Ahold is a variant of the noun hold, used in such sentences as “I’ll get ahold of you later.” But when you mean to refer to an actual grip on something, use two words: “She really has a hold on you.” If it’s hard to decide which form to employ, try this test: If you can insert an adjective between a and hold, the two-word form is appropriate.

2. Already/all ready: Use the former when you need an adverb, as in “I told you already.” The latter form is correct in sentences such as “We’re all ready for the party.”

3. Alot/a lot: These two forms are interchangeable except in one significant respect: The one-word version is wrong. It is used often in informal writing and may one day be standard, but until you get the official memo, refrain from using it if you want to be taken seriously as a writer.

4. Alright/all right: See item number 3.

5. Altogether/all together: The one-word form, an adverb, suffices to mean “completely” or “in total,” as in “Altogether, we saved $100 on the deal.” (It also means “nude” in the idiomatic phrase “in the altogether.”) The phrase is appropriate for sentences such as “We are all together in this.”

6. Anybody/any body: The on-word form is a pronoun used in such constructions as “He doesn’t get along with anybody.” The two-word adjective-noun form is applicable in limited contexts, such as in the sentence “Any body in motion responds to gravity.”

7. Anymore/any more: The one-word form is used as an adverb in sentences such as “We don’t go there anymore”; the two-word form consists of the adjective any and the noun more, as in “I just can’t eat any more of that pie.”

8. Anyone/any one: The one-word form is a pronoun, synonymous with anybody, used as in “Anyone can make that claim.” “Any one” consists of the adjective any and the noun one, as in “Any one of you might be next.”

9. Anyplace/any place: The adverb anyplace is a synonym for anywhere: “She won’t let me go anyplace without her.” The latter usage is an adjective-and-noun phrase that describes a location: “He doesn’t want to go to any place he can’t smoke.”

10. Anything/any thing: Anything is the likely usage: “I don’t remember anything.” The two-word adjective-noun form is generally separated by an another adjective: “She’s just does any little thing she wants.”

11. Anytime/any time: To describe with what frequency something might occur, use the one-word adverbial form: “Stop by anytime.” The two-word adjective-noun form is preceded by the word at: “You may leave at any time.”

12. Anyway/any way: Anyway is a synonym for anyhow: “We didn’t want to go anyway.” The two-word adjective-noun form is preceded by the word in: “That doesn’t change the results in any way.”

13. Awhile/a while: The noun phrase “a while” and the adverb awhile are virtually interchangeable in a sentence, though you should precede the two-word form with the word for: “I think I’ll sit here for a while” and “I think I’ll sit here awhile” mean the same thing.

14. Cannot/can not: Cannot is virtually the only proper alternative. The second usage is wrong except in the correct awkward construction in the sentence “I can not go,” meaning “I can decide not to go.”

15. Everyday/every day: The one-word form is an adjective meaning “ordinary,” used to describe something usual as in “These are my everyday clothes.” The two-word phrase, an adverb, is used in such sentences as “I go there every day” to explain how something is done.

16. Everyone/every one: To refer to everybody, use one word: “Everyone’s a critic.” To emphasize a single individual or item, use two words: “Every one of them is broken.”

17. Everything/every thing: Everything is the default choice: “You’ve ruined everything.” The two-word adjective-noun form is usually divided by an additional adjective: “Every little thing she does is magic.”

18. Maybe/may be: The first choice is an alternative to the adverb perhaps; the second is a verb phrase used in such sentences as “It may be that she was right after all.”

19. Overtime/over time: As one word, this means word done beyond a regular shift: “I’ve worked overtime several days this week.” As two words, it refers to the passage of time: “Over time, we’ve seen dramatic changes.”

20. Sometime/some time: The one-word form is an adverb describing vagueness about when something will happen, as in “I’ll get around to it sometime.”

1. Ad lib (from ad libitum): an improvisation
2. Baroque: elaborate, extravagant, and/or flamboyant
3. Beat: a brief measure or pause
4. Cadence: a sequence or measure of rhythm
5. Choir: a group of people sharing beliefs or values (“preaching to the choir”)
6. Chord: the target of a stimulus (“strike a chord”)
7. Chorus: a unified response (“a chorus of approval”)
8. Coda: a conclusion
9. Conductor: someone who organizes an enterprise or scheme
10. Crescendo: a high point
11. Cue: a signal to start or do something or cause it to happen
12. Downbeat: pessimistic
13. Duet: an action undertaken by a union of two people
14. Encore: an additional performance or achievement
15. Ensemble: a group in which no one person stands out
16. Falsetto: an unnaturally high voice
17. Fanfare: celebratory attention
18. Finale: a concluding performance or act
19. Gig: a job or assignment
20. Impromptu: spontaneous, improvised
21. Interlude: a planned interruption or intervening period
22. Leitmotif: a recurring overarching idea
23. Maestro: an accomplished person
24. Medley: a series or other collection of ingredients or actions
25. Opera: extended to “soap opera,” the slang term for domestic radio and later television dramas (so called because detergent manufacturers often sponsored these programs aimed at homemakers) and “horse opera,” another name for westerns (plural of opus)
26. Opus: a major work
27. Orchestrate: to organize strategically, with a possible connotation of conniving or conspiracy
28. Overtone: a suggestion or connotation
29. Overture: an invitation or act of persuasion
30. Pitch: the nature of a sound based on its frequency, or a degree of interest (“fever pitch”)
31. Prelude: a preliminary to a main action
32. Prologue: an introduction
33. Reprise: a repeated performance
34. Requiem: a composition in any medium to honor the dead or a failed effort
35. Resonance: an evocation of feeling or sense
36. Rhapsodic: any overwrought or elaborate creative effort or speech (“waxing rhapsodic”)
37. Riff: a verbal performance, especially as in a fast and furious routine by a stand-up comedian; also refers to a brief witticism or to a variation, synonymous with the informal noun take
38. Rock: to be very impressive or pleasing (“That rocks!”), to inspire excitement (“The band rocked the concert hall”), or to flaunt an ostentatious style of clothing or coiffure (“She rocked her new boots”)
39. Serenade: an effort to persuade
40. Solo: alone
41. Staccato: a suggestion of speed rather than simply detached sounds (“staccato bursts of gunfire”)
42. Suite: a collection or set
43. Tempo: speed or rate
44. Theme: subject or style
45. Timbre: the distinguishing quality of a voice
46. Tone: the quality of expression in writing or speaking as well, and the quality of a physical form
47. Unison: agreement or union
48. Upbeat: optimistic
49. Virtuoso: one particularly skilled in an endeavor
50. Waltz: to move in a bold, confident, or lively manner (“She triumphantly waltzed into the room”)

1. Acronyms: An acronym is an abbreviation consisting of a string of initial letters pronounced as a word. Fictional examples, such as SPECTRE (for “Special Executive for Counter-intelligence, Terrorism, Revenge, and Extortion”), from the James Bond novels and films, and VILE (for “Villains’ International League of Evil”), from the Carmen Sandiego computer-game series, can be serious or humorous depending on formation and intent.

2. Anagrams: An anagram is simply a word with its letters scrambled in a new order. Many humorous phrases have been derived by scrambling expressions or people’s names, such as forming “I am a weakish speller” from “William Shakespeare.” (Anagram generators can be found on the Internet.)

3. Chronograms: A chronogram is a phrase in which constituent letters also express a number, as in “My Day Closed Is In Immortality,” an epitaph for England’s Queen Elizabeth I in which the first letter of each word corresponds to a Roman numeral; the numerical sequence, MDCIII, is translated as 1603, the date of her death. A weak variant is a habit of filmmakers (or, more accurately, film marketers) of replacing one or more letters in a movie title with a number vaguely resembling the letter or otherwise related, as in the title of the 1995 crime thriller Seven, represented on posters as Se7en.

4. Initialisms: Initialisms are distinguished from acronyms by the fact that the constituent letters are pronounced individually, rather than sequentially sounded as if they were a single word. Many popular social-networking terms such as LOL (“laugh out loud”) and ROTFL (“roll on the floor laughing”) are initialisms; so is TEOTWAWKI (“the end of the world as we know it”).

5. Lipograms: A lipogram is a composition deliberately consisting of words lacking a letter of the alphabet. Such a work is more or less easily accomplished depending on the letter selected for omission; many writers, astonishingly, have written novels produced without recourse to use of a common letter such as e or t.

6. Malapropisms: This type of wordplay refers to misuse of one word for another by those too ignorant to recognize the error. It’s named after Mrs. Malaprop, a character in an eighteenth-century play who is notorious for such unwitting utterances, as exemplified by the character’s line “She’s as headstrong as an allegory on the banks of Nile.” Shakespeare also employed such humor, most notably in lines by the character Dogberry in Much Ado About Nothing such as “Our watch, sir, have indeed comprehended two auspicious persons.”

7. Mondegreens: Misunderstood song lyrics are often referred to as mondegreens; the term itself is based on a mishearing of the phrase “laid him on the green.” A more recent example is “Excuse me while I kiss this guy,” rather than “Excuse me while I kiss the sky,” from the Jimi Hendrix song “Purple Haze.”

8. Onomatopoeias: Onomatopoeias (the term is from the Greek words for “make” and “name”) are words that imitate sounds, such as splash or bump. A notable example of an onomatopoeic proper name is that of the Houyhnhnms, the sentient, civilized horses from Jonathan Swift’s Gulliver’s Travels.

9. Portmanteaus: Portmanteaus, words creating by combining two words and their meanings into one, were named and popularized by Lewis Carroll. He coined several, such as slithy (from lithe and slimy); more recent examples include brunch and smog. (Carroll named the form of wordplay after a word for a suitcase with two separate compartments.)

10. Spoonerisms: The term for expressions in which initial letters, or sometimes entire syllables or words, are transposed is based on the name of a British clergyman supposedly prone to such utterances, though many attributed to him were only inspired by him. Among them is “a well-boiled icicle” for “a well-oiled bicycle”; John Lennon is credited with coining a variation on “Time heals all wounds”: “Time wounds all heels.”