Erosion of distinctions between senses for words with similar or related meanings is a natural process, but careful writers resist becoming accessories to acceleration of that process. Here are ten word pairs that are used interchangeably, often at the expense of clarity.
1. Accurate/precise: Accuracy is the degree to which an estimated measurement or a predicted result matches the actual extent or outcome, or, in the context of aiming, how close a projectile or an effect (such as a laser beam) comes to an intended target. Precision is the degree of variation between or among two or more measurements. In competition in which relative skill is determined by having competitors hit a bull’s-eye target, a competitor may demonstrate precision (all attempts are in proximity to each other) but not accuracy (the attempts are far from the center of the target).
2. Allude/refer: The distinction between allusion and reference is one of degree of fidelity to the source. If one refers to a well-known saying, one says or writes, “The early bird catches the worm.” An allusion, however, is indirect; one might say or write, “I caught the worm this morning,” which, if one’s audience knows the saying, they will understand to mean that one was early.
3. Anxious/eager: One who is anxious about something is, according to the source of the adjective, experiencing anxiety, while one who is eager is excited, impatient, and/or interested. Many people use the words interchangeably to refer to a positive feeling, but careful writers will maintain the distinction.
4. Amount/number: Amount applies to uncountable nouns, such as in general reference to noise, while number pertains to a measurable quantity, such as how many decibels a sound registers. Another comparison is between a reference to an amount of money, such as a million dollars, which is a single “item,” as opposed to the count of the number of bills in a stack of currency.
5. Convince/persuade: To convince someone is to cause that person to accept a truth, while to persuade is to cause someone, through reasoning or argument, to do something. Thus, the distinction is between influencing thought and prompting action.
6. Ensure/insure: To ensure is to guarantee, while insure has a more specific sense of indemnity against loss, but the latter word is widely used in the sense expressed by the former word. (Assure, with the same root, means “convince or give confidence” and is also often employed as a lazy substitute for ensure.)
7. Fewer/less: As with amount and number, the distinction between fewer and less is one of countable and uncountable things, in that order. For example, one would write, “Fewer houses were built this year compared to last year,” but “Less housing is available his year compared to last year”; the first sentence refers to countable structures and the second one pertains to houses collectively.
8. Figuratively/literally: Figuratively pertains to hyperbolic or metaphorical references, while literally means “in an exact or strict sense,” but many people misuse the latter word as an intensifier when they intend to convey the sense of the former word, as in “My head literally exploded when she said that!” One who literally experienced such a phenomenon would no longer be alive to report it.
9. Libel/slander: Both libel and slander are, in legal usage, acts of defamation—communication of a falsehood that damages an entity’s reputation—but libel is written expression, while slander is an oral statement.
10. Poisonous/venomous: In literal usage, the distinction is one of delivery—poison produced by living things acts on an individual when one eats or touches it, and chemical poisons, though they may be administered by a person to another, do not themselves “choose” to poison the victim. By contrast, venom is injected into its victim by a bite or a sting from another animal, either in self-defense or in an attack on prey by a predator. Figuratively, poisonous describes a psychologically dysfunctional environment or person, while venomous applies only to an individual, often one who is malevolent or spiteful.
Two other word pairs that deserve distinction are if and whether and what and which: In the case of if and whether, if is employed when describing a condition, as in “I will take a river cruise on the Seine if I visit Paris,” and whether denotes a choice or a doubt, as in “I don’t know whether I will (or “will have time to”) take a river cruise on the Seine when I visit Paris.” In conversation and in informal writing, if is acceptable in the latter senses, but in formal writing, use whether. Likewise, which is a more specific usage that what when referring to particular selections: “I don’t know which outfits I’m going to pack” is preferable to “I don’t know what outfits I’m going to pack.”