Terms for members of the aristocracy are often applied by extension to other, often colloquial, usage. Here are titles of English nobility and some of their other connotations.
King, from the Old English word cyning, refers to a hereditary lifelong ruler; a king who rules over other kings might be called a high king. The word emperor, from the Latin term imperator, meaning “commander,” denoted someone who ruled over an empire, a collection of kingdoms or other states, though it was never used in England or Great Britain. Female equivalents are queen and empress; monarch is a non-gender-specific generic term not used as a title with a name (as king or emperor would be in, say, “King Arthur” or “Emperor Hirohito”).
King is also used to describe the preeminent person in a field, as in Michael Jackson’s designation as “the King of Pop.” (Jazz musicians of the early twentieth century were precursors of this tradition, adopting monikers such as Duke Ellington and Count Basie that referred to their stature as leading practitioners of their craft. It is also the name of a playing card, a chess piece, and a crowned piece in checkers; emperor has no such connotations, though both king and emperor are sometimes applied to large animals of their type, as in “king penguin” and “emperor penguin,” and “monarch butterfly” refers to an especially regal-looking specimen of flying insect.
Queen, meanwhile, has other meanings: It refers to a woman of regal bearing or of attainment of stature in an area of endeavor, such as in “beauty queen,” or to an animal, such as a type of bee, that exists for breeding. The word is also applied, often pejoratively, to an effeminate or flamboyant gay man, or, in the phrase “drama queen,” to a highly emotional person. Queen also refers to a specific playing card and a particular chess piece.
The Latin term princeps (“first citizen”) was originally applied to the unofficial leader of the Roman Senate; later, the emperor Augustus referred to his grandsons by that title, and as prince in English it came to refer to the male descendants of a king. (An heir to a kingship is a crown prince.) It is also used generically, as in the title of Niccolò Machiavelli’s classic political tract The Prince, to refer to any political leader of noble birth.
A prince might also be the ruler of a small country (called a principality), as was common in Europe during the early 1800s, or the husband of a ruling queen. The feminine form is princess, which is also sometimes used jocularly to be a spoiled woman or girl, while prince was at times used as an obsequious compliment for a man of high professional or social standing.
The Latin word dux (“leader”), from which duke was derived, was used to refer to a military commander, especially a non-Roman one, in the Roman Republic and later the top military commander of a Roman province. From there the sense became that of a ruler of a province (and sometimes a separate country, styled a duchy). Eventually, the title was granted to a few senior nobles, including, in England, the king’s sons. In other countries, a preeminent duke might be styled an archduke or a grand duke; the female equivalent of a duke, or the wife of one, is a duchess. (John Wayne’s nickname, Duke, derived from the name of a favorite dog of his.)
A marquis (the English equivalent is a marquess, pronounced as spelled) was a nobleman whose domain was on the march, or border, of a country, and therefore had higher status than the next-highest-ranking nobleman, a count. (The female equivalent is a marquise, or marchioness.) The title of count derives from the Latin term comitem (“companion”), which refers to an associate or representative of an emperor; from this word we get county, originally referring to the area held by a count.
The equivalent to count in the British Isles is earl (from the Old English term eorl, meaning “nobleman” or “warrior”), but because no feminine equivalent of that term exists, countess is used for both the wife of a count and the wife of an earl. (Earl is also a given name.) Viscount (the first element of the word is from vice, as in “vice president”) is a term for a lower-ranking nobleman; viscountess is the feminine equivalent.
The lowest-ranking title of nobility is baron, from a Latin word for “man,” “servant,” or “soldier”; a baron held a barony, and his wife was a baroness. Baronet is a title granted by kings of England, but baronets (and their wives, called baronetesses) are not considered of the nobility. By extension, baron has been used to denote to a person of influence in commerce, such as in “cattle baron,” referring to a wealthy rancher.
The rank of knight formerly denoted the bottom tier of nobility, but it is no longer conferred except as an honorary title in England, although hereditary knighthoods persist in other European countries. “White knight” and “black knight” refer in business lingo to someone seeking to acquire a corporation in a friendly or unfriendly takeover respectively; “knight in shining armor” is a dated reference to an ideal man sought by a woman as good marriage material. The female equivalent of knight is dame, which also used to be applied to an elderly woman in general and for a time during the twentieth century was slang for an attractive woman.
The wife of a king who does not herself rule is referred to as a queen consort or empress consort; a woman who rules is a queen regnant or empress regnant. The widow of any nobleman is called a dowager (the word is from the Middle French term douagiere, derived from douer, meaning “to endow”); this term, like the others used in association with a higher-ranking title in a phrase such as “queen dowager,” may also refer to any woman holding property from her deceased husband, or to a dignified elderly woman in general, though such usage is rare, and the latter is generally meant humorously.