mid-14c., "fluid or juice of an animal or plant," from Old North French humour "liquid, dampness; (medical) humor" (Old French humor, umor; Modern French humeur), from Latin umor "body fluid" (also humor, by false association with humus "earth"); related to umere "be wet, moist," and to uvescere "become wet" (see humid).

In old medicine, "any of the four body fluids" (blood, phlegm, choler, and melancholy or black bile).

The human body had four humors—blood, phlegm, yellow bile, and black bile—which, in turn, were associated with particular organs. Blood came from the heart, phlegm from the brain, yellow bile from the liver, and black bile from the spleen. Galen and Avicenna attributed certain elemental qualities to each humor. Blood was hot and moist, like air; phlegm was cold and moist, like water; yellow bile was hot and dry, like fire; and black bile was cold and dry, like earth. In effect, the human body was a microcosm of the larger world. [Robert S. Gottfried, "The Black Death," 1983]

 Their relative proportions were thought to determine physical condition and state of mind. This gave humor an extended sense of "mood, temporary state of mind" (recorded from 1520s); the sense of "amusing quality, funniness, jocular turn of mind" is first recorded 1680s, probably via sense of "whim, caprice" as determined by state of mind (1560s), which also produced the verb sense of "indulge (someone's) fancy or disposition." Modern French has them as doublets: humeur "disposition, mood, whim;" humour "humor." "The pronunciation of the initial h is only of recent date, and is sometimes omitted ..." [OED].

For aid in distinguishing the various devices that tend to be grouped under "humor," this guide, from Henry W. Fowler ["Modern English Usage," 1926] may be of use:

HUMOR: motive/aim: discovery; province: human nature; method/means: observation; audience: the sympathetic

WIT: motive/aim: throwing light; province: words & ideas; method/means: surprise; audience: the intelligent

SATIRE: motive/aim: amendment; province: morals & manners; method/means: accentuation; audience: the self-satisfied

SARCASM: motive/aim: inflicting pain; province: faults & foibles; method/means: inversion; audience: victim & bystander

INVECTIVE: motive/aim: discredit; province: misconduct; method/means: direct statement; audience: the public

IRONY: motive/aim: exclusiveness; province: statement of facts; method/means: mystification; audience: an inner circle

CYNICISM: motive/aim: self-justification; province: morals; method/means: exposure of nakedness; audience: the respectable

SARDONIC: motive/aim: self-relief; province: adversity; method/means: pessimism; audience: the self

1530s, abbreviation of videlicet "that is to say, to wit, namely" (mid-15c.), from Latin videlicet, "evidently, of course," contraction of videre licet "it is permissible to see," from videre "to see" (see vision) + licet "it is allowed," third person singular present indicative of licere "be allowed" (see licence). The -z- is not an alphabetic letter, but originally a twirl, representing the usual Medieval Latin shorthand symbol for the ending -et. "In reading aloud usually rendered by 'namely.' " [OED]

"having the power of judging or discerning rightly," Old English wis "learned, sagacious, cunning; sane; prudent, discreet; experienced, practically knowing;" from Proto-Germanic *wissaz, reconstructed to be from past-participle adjective *wittos of PIE root *weid- "to see" (hence "to know;" compare wise (n.)).

The word is related to the source of Old English witan "to know, be aware of" (see wit (v.)). In Middle English also used in reference to a trade or craft, to warfare; an animal good at tracking by scent was wise of nese. Germanic cognates include Old Saxon, Old Frisian wis, Old Norse viss, Dutch wijs, German weise "wise."

The modern slang meaning "aware, cunning" is attested by 1896.

A wise man has no extensive knowledge; He who has extensive knowledge is not a wise man. [Lao-tzu, "Tao te Ching," c. 550 B.C.E.]

Wise man "man of good discernment" was in Old English; wise guy is attested from 1896, American English, ironic, "know-it-all; maker of wisecracks." Wise-ass (n.) is by 1966, American English (probably a literal sense is intended by the phrase in the 1607 comedy "Westward Hoe" by Dekker and Webster).

As a noun, "persons endowed with reason or prudence," by c. 1200. The use in phrases such as none or never the wiser la by late 14c. (lytel am I þe wyser).

Wisenheimer, with mock German or Yiddish surname suffix is by 1900 (it also is an actual surname).

"to know" (archaic), c. 1500, a spurious word from the past tense of wit (v.) "to know" improperly used as present indicative (in place of wists). It is cognate with German wusste, past tense of wissen "to know."

Had-I-wiste was used c. 1400-1550 in sense "regret for something done rashly or heedlessly;" see wist. Proverbial in expression Had-I-wiste cometh ever too late.

Haddywyst comyth euer to late Whan lewyd woordis beth owte y-spronge. ["Commonplace book" in Trinity College, Cambridge, c. 1500]

also dim-wit, "slow-witted person," U.S. college slang by 1922, from dim (adj.) "of low intensity" + wit (n.) "intelligence." Related: dimwitted; dimwittedly.

"fool, idiot," slang, c. 1970, originally British or Australian English, from fuck + wit (n.).

"simpleton" (one lacking all his wits), 1755, from half + wit (n.). Earlier "a would-be wit whose abilities are mediocre" (1670s).

Half-wits are fleas; so little and so light,

We scarce could know they live, but that they bite.

[Dryden, "All for Love"]

Phrase out of half wit "half out of one's mind" was in Middle English (late 14c.). Half-witted "lacking common sense" is from 1640s.

"inward awareness of right or wrong" (a word formed to translate Latin conscientia), early 13c., "conscience;" c. 1300, "reason, intellect," from in (adj.) + wit (n.).

Þese ben also þy fyve inwyttys: Wyl, Resoun, Mynd, Ymaginacioun, and Thoght [Wycliffe, c. 1380]

Not related to Old English inwit, which meant "deceit." Joyce's use of it in "Ulysses" (1922) echoes the title of the 14c. work "Ayenbite of Inwyt" ("Remorse of Conscience," a translation from French) and is perhaps the best-known example of the modern use of the word as a conscious archaism, but it is not the earliest.

If ... such good old English words as inwit and wanhope should be rehabilitated (and they have been pushing up their heads for thirty years), we should gain a great deal. [Robert Bridges, English poet laureate, 1922]

Old English cnawan (class VII strong verb; past tense cneow, past participle cnawen), "perceive a thing to be identical with another," also "be able to distinguish" generally (tocnawan); "perceive or understand as a fact or truth" (opposed to believe); "know how (to do something)," from Proto-Germanic *knew- (source also of Old High German bi-chnaan, ir-chnaan "to know"), from PIE root *gno- "to know."

For pronunciation, see kn-. Once widespread in Germanic, the verb is now retained there only in English, where it has widespread application, covering meanings that require two or more verbs in other languages (such as German wissen, kennen, erkennen and in part können; French connaître "perceive, understand, recognize," savoir "have a knowledge of, know how;" Latin scire "to understand, perceive," cognoscere "get to know, recognize;" Old Church Slavonic znaja, vemi). The Anglo-Saxons also used two distinct words for this, the other being witan (see wit (v.)).

From c. 1200 as "to experience, live through." The meaning "to have sexual intercourse with," also found in other modern languages, is attested from c. 1200, from the Old Testament (Genesis iv.1). Attested from 1540s in colloquial phrases suggesting cunning or savvy (but often in the negative).

As far as (one) knows "to the best of (one's) knowledge" is late 14c. Expression God knows is from c. 1400. To know too much (to be allowed to live, escape, etc.) is from 1872. To know better "to have learned from experience" is from 1704.

As an expression of surprise, what do you know attested by 1914. Don't I know it in the opposite sense ("you need not tell me") is by 1841.

also nit-wit, "stupid person," by 1914, American English slang, probably from nit "nothing," from dialectal German or Yiddish, from Middle Low German (see nix (n.)) + wit (n.). Related: Nitwitted; nitwittery.