Online Etymology Dictionary

recognize (v.): early 15c., "resume possession of land," back-formation from recognizance, or else from Old French reconoiss-, stem of reconoistre "to know again, identify, recognize," from Latin recognoscere "acknowledge, recall to mind, know again; examine; certify," from re- "again" (see re-) + cognoscere "to get to know, recognize" (see cognizance). Meaning "know again, recall or recover the knowledge of, perceive an identity with something formerly known or felt" first recorded 1530s. Related: Recognized; recognizing.
scienter (adv.): legalese Latin, literally "knowingly," from sciens, present participle of scire "to know" (see science) + adverbial suffix -ter.
heard: past tense and past participle of hear, Old English herde. To have heard of "know about" is from 1907.
doohickey (n.): also doohicky, a name for something one doesn't know the name of, 1914, American English, arbitrary formation.
je ne sais quoi (n.): "an inexpressible something," French, literally "I do not know what."
[T]hey are troubled with the je-ne-scay-quoy, that faign themselves sick out of niceness but know not where their own grief lies, or what ayls them. [Thomas Blount, "Glossographia," 1656]
-oid: word-forming element meaning "like, like that of, thing like a ______," from Latinized form of Greek -oeides, from eidos "form," related to idein "to see," eidenai "to know;" literally "to see," from PIE *weid-es-, from root *weid- "to see, to know" (see vision). The -o- is connective or a stem vowel from the previous element.
Veda (n.): ancient sacred Hindu book, 1734, from Sanskrit veda, literally "knowledge, understanding," especially "sacred knowledge," from root vid- "to know," from PIE root *weid- "to see" (related to wit, and to Avestan vaeda "I know," Latin videre "to see;" see vision (n.)). The books are the Rig-, Yajur-, Sama-, and Atharva-veda.
vision (n.): c. 1300, "something seen in the imagination or in the supernatural," from Anglo-French visioun, Old French vision "presence, sight; view, look, appearance; dream, supernatural sight" (12c.), from Latin visionem (nominative visio) "act of seeing, sight, thing seen," noun of action from past participle stem of videre "to see."

This is from the productive PIE root *weid- "to know, to see" (source also of Sanskrit veda "I know;" Avestan vaeda "I know;" Greek oida, Doric woida "I know," idein "to see;" Old Irish fis "vision," find "white," i.e. "clearly seen," fiuss "knowledge;" Welsh gwyn, Gaulish vindos, Breton gwenn "white;" Gothic, Old Swedish, Old English witan "to know;" Gothic weitan "to see;" English wise, German wissen "to know;" Lithuanian vysti "to see;" Bulgarian vidya "I see;" Polish widzieć "to see," wiedzieć "to know;" Russian videt' "to see," vest' "news," Old Russian vedat' "to know").

The meaning "sense of sight" is first recorded late 15c. Meaning "statesman-like foresight, political sagacity" is attested from 1926.
connoisseur (n.): 1714, from French connoisseur (Modern French connaiseur), from Old French conoisseor "an expert, a judge, one well-versed," from conoistre "to know," from Latin cognoscere "to get to know, recognize, become well-acquainted with," from com- "with" (see com-) + gnoscere "recognize" (see notice (v.)).
savoir-faire (n.): "instinctive knowledge of the right course of action in any circumstance," 1815, from French, literally "to know (how) to do," from savoir "to know" (from Latin sapere; see sapient) + faire (from Latin facere "to make, do;" see factitious). French also has savoir-vivre "ability in good society; knowledge of customs in the world."
agnosticism (n.): 1870, from agnostic + -ism.
The agnostic does not simply say, "I do not know." He goes another step, and he says, with great emphasis, that you do not know. [Robert G. Ingersoll, "Reply to Dr. Lyman Abbott," 1890]
kunst (n.): from German Kunst "art," originally "knowledge, skill" (9c.), abstract noun from the root of kennen "to know," können "know how, be able" (see can (v.)). Appearing in English in various compounds from 1899, never quite nativized.
wit (v.): "to know" (archaic), Old English witan (past tense wast, past participle witen) "to know, beware of or conscious of, understand, observe, ascertain, learn," from Proto-Germanic *witan "to have seen," hence "to know" (source also of Old Saxon witan, Old Norse vita, Old Frisian wita, Middle Dutch, Dutch weten, Old High German wizzan, German wissen, Gothic witan "to know"), from PIE *weid- (see wit (n.)). The phrase to wit, almost the only surviving use of the verb, is first recorded 1570s, from earlier that is to wit (mid-14c.), probably a loan-translation of Anglo-French cestasavoir, used to render Latin videlicet (see viz.).
wittol (n.): "compliant cuckold," late 15c., witewold, probably from witen "to know" (see wit (v.)) + ending from noun cuckold (Middle English cokewold).
acquaint (v.): early 13c., from Old French acointier "make known, make acquaintance of," from Vulgar Latin accognitare "to make known," from Latin accognitus "acquainted with," past participle of accognoscere "know well," from ad- "to" (see ad-) + cognitus, past participle of cogniscere "come to know," from com- "with" (see com-) + gnoscere "know" (see notice (n.)). Originally reflexive, "to make oneself known;" sense of "to gain for oneself personal knowledge of" is from early 14c. Related: Acquainted; acquainting.
cognizance (n.): mid-14c., from Anglo-French conysance "recognition," later, "knowledge," from Old French conoissance "acquaintance, recognition; knowledge, wisdom" (Modern French connaissance), from past participle of conoistre "to know," from Latin cognoscere "to get to know, recognize," from com- "together" (see co-) + gnoscere "to know" (see notice (n.)). The -g- was restored in English spelling 15c. and has gradually affected the pronunciation, which was always "con-." The old pronunciation lingered longest in legal use.
wiseacre (n.): 1590s, partial translation of Middle Dutch wijssegger "soothsayer" (with no derogatory connotation), probably altered by association with Middle Dutch segger "sayer" from Old High German wizzago "prophet," from wizzan "to know," from Proto-Germanic *wit- "to know" (see wit (v.)). The deprecatory sense of "one who pretends to know everything" may have come through confusion with obsolete English segger "sayer," which also had a sense of "braggart" (mid-15c.).
savvy (n.): 1785, "practical sense, intelligence;" also a verb, "to know, to understand;" West Indies pidgin borrowing of French savez(-vous)? "do you know?" or Spanish sabe (usted) "you know," both from Vulgar Latin *sapere, from Latin sapere "be wise, be knowing" (see sapient). The adjective is first recorded 1905, from the noun. Related: Savvily; savviness.
wist (v.): "to know" (archaic), c. 1500, from Old English past tense of witan "to know" (cognate with German wusste, past tense of wissen "to know"); see wit. 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]
scilicet: late 14c., Latin, "you may know, you may be sure, it is certain," used in sense "that is to say, namely," contraction of scire licit "it is permitted to know," from scire "to know" (see science); for second element see licit. Used as was Old English hit is to witanne, literally "it is to wit" (see wit (v.)). Often abbreviated sc. or scil.
Its function is to introduce : (a) a more intelligible or definite substitute, sometimes the English, for an expression already used ... (b) a word &c. that was omitted in the original as unnecessary, but is thought to require specifying for the present audience .... [Fowler]
cunning (adj.): early 14c., "learned, skillful," present participle of cunnen "to know" (see can (v.1)). Sense of "skillfully deceitful" is probably late 14c. As a noun from c. 1300. Related: Cunningly.
diagnosis (n.): 1680s, medical Latin application of Greek diagnosis "a discerning, distinguishing," from stem of diagignoskein "discern, distinguish," literally "to know thoroughly," from dia- "apart" (see dia-) + gignoskein "to learn" (see gnostic).
dingus (n.): "any unspecified or unspecifiable object; something one does not know the name of or does not wish to name," 1876, U.S. slang, from Dutch dinges, literally "thing" (see thing).
almah (n.): Egyptian dancing-girl, belly-dancer, 1814, perhaps from Arabic almah (fem. adjective), "learned, knowing," from alama "to know." Or perhaps from a Semitic root meaning "girl" (source also of Hebrew alma "a young girl, a damsel").
precognition (n.): "foreknowledge," mid-15c., from Late Latin praecognitionem (nom. praecognitio), noun of action from past participle stem of Latin praecognoscere "to foreknow," from prae "before" (see pre-) + cognoscere "to get to know, recognize" (see cognizance).
Sturmabteilung (n.): 1923, from German, literally "storm detachment;" paramilitary force of the Nazi Party, founded 1921, repressed 1934, also know by its initials, S.A.; also see Brown Shirt.
Pima: Uto-Aztecan people of Arizona, from Spanish, probably from native pi ma:c "(I) don't know," given in answer to some question long ago and mistaken by the Spaniards as a tribal name. Related: Piman.
sciolist (n.): 1610s, "smatterer, pretender to knowledge," from Late Latin sciolus "one who knows a little," diminutive of scius "knowing," from scire "to know" (see science) + -ist. Related: Sciolistic.
foreknowledge (n.): "prescience," 1530s, from fore- + knowledge. Earlier in this sense was foreknowing (late 14c.), from foreknow "have previous knowledge of, know beforehand." Old English had forewitan, Middle English forwiten "to foreknow."
cognitive (adv.): 1580s, from Latin cognit-, past participle stem of cognoscere "to get to know, recognize" (see cognizance) + -ive. Taken over by psychologists and sociologists after c. 1940. Related: Cognitively.
cognoscente (n.): "connoisseur," 1778, from Italian cognoscente, Latinized from conoscente "connoisseur," literally "knowing man," from Latin cognoscentum (nominative cognoscens), present participle of cognoscere "to get to know, recognize" (see cognizance).
witness (v.): c. 1300, "bear testimony," from witness (n.). Meaning "affix one's signature to (a document) to establish its identity" is from early 14c. Meaning "see or know by personal presence, observe" is from 1580s. Related: Witnessed; witnessing.
hepcat (n.): also hep-cat, "addict of swing music," more generally, "one who is in the know and knows it," 1937, from hep (1) "aware, up-to-date" in jazz slang + cat (n.) "jazz enthusiast."
ignore (v.): 1610s, "not to know, to be ignorant of," from French ignorer "be unaware of" (14c.), or directly from Latin ignorare "not to know, be unacquainted; take no notice of, disregard" (see ignorant). The original sense in English is obsolete. Sense of "pass over without notice, pay no attention to" in English first recorded 1801 (Barnhart says "probably a dictionary word"), and OED indicates it was uncommon before c. 1850. Related: Ignored; ignoring.
prognosis (n.): 1650s, "forecast of the probable course of a disease," from Late Latin prognosis, from Greek prognosis "foreknowledge," also, in medicine, "predicted course of a disease," from stem of progignoskein "come to know beforehand," from pro- "before" (see pro-) + gignoskein "come to know" (see gnostic). General (non-medical) use in English from 1706. A back-formed verb prognose is attested from 1837. Related: Prognosed; prognosing.
wizard (n.): early 15c., "philosopher, sage," from Middle English wys "wise" (see wise (adj.)) + -ard. Compare Lithuanian zynyste "magic," zynys "sorcerer," zyne "witch," all from zinoti "to know." The ground sense is perhaps "to know the future." The meaning "one with magical power, one proficient in the occult sciences" did not emerge distinctly until c. 1550, the distinction between philosophy and magic being blurred in the Middle Ages. As a slang word meaning "excellent" it is recorded from 1922.
multiverse (n.): 1895, William James's coinage, an alternative to universe meant to convey absence of order and unity.
But those times are past; and we of the nineteenth century, with our evolutionary theories and our mechanical philosophies, already know nature too impartially and too well to worship unreservedly any god of whose character she can be an adequate expression. Truly all we know of good and beauty proceeds from nature, but none the less so all we know of evil. Visible nature is all plasticity and indifference, a moral multiverse, as one might call it, and not a moral universe. [William James, "Is Life Worth Living?" address to the Young Men's Christian Association of Harvard University, May 1895]
Gwendolyn: fem. proper name; the first element is Breton gwenn "white" (source also of Welsh gwyn, Old Irish find, Gaelic fionn, Gaulish vindo- "white, shining," literally "visible"), from nasalized form of PIE root *weid- "to see, know" (see vision).
Rig veda: 1776, from Sanskrit rigveda, from rg- "praise, hymn, spoken stanza," literally "brightness," from PIE *erkw- "to radiate, beam; praise" + veda "knowledge," from PIE *weid-o-, from root *weid- "to know, see" (see vision (n.)). A thousand hymns, orally transmitted, probably dating from before 1000 B.C.E. Related: Rig-vedic.
savant (n.): "one eminent for learning," 1719, from French savant "a learned man," noun use of adjective savant "learned, knowing," former present participle of savoir "to know," from Vulgar Latin *sapere, from Latin sapere "be wise" (see sapient).
gnosis (n.): "knowledge," especially "special knowledge of spiritual mysteries," 1703, from Greek gnosis "a knowing, knowledge; a judicial inquiry, investigation; a being known," in Christian writers, "higher knowledge of spiritual things," from PIE *gno-ti-, from root *gno- "to know" (see gnostic (adj.)).
white elephant (n.): "burdensome charge, inconvenient thing that one does not know how to get rid of," 1851, supposedly from the practice of the King of Siam of presenting one of the sacred albino elephants to a courtier who had fallen from favor; the gift was a great honor, but the proper upkeep of one was ruinously expensive.
serviceable (adj.): "ready to do service," early 14c., from Old French servicable, from servise (see service (n.1)). Related: Serviceability.
Edgar: I know thee well: a serviceable villain,
As duteous to the vices of thy mistress
As badness would desire.
["King Lear," IV.vi.]
ignoramus (n.): 1570s, originally an Anglo-French legal term (early 15c.), from Latin ignoramus "we take no notice of, we do not know," first person plural present indicative of ignorare "not to know, take no notice of" (see ignorant). The legal term was one a grand jury could write on a bill when it considered the prosecution's evidence insufficient. Sense of "ignorant person" (1616) came from the title role in George Ruggle's 1615 play in Latin satirizing the ignorance of common lawyers. The plural is ignoramuses as it never was a noun in Latin.
twitterpated (adj.): 1942, apparently first attested in the Walt Disney movie "Bambi" (there also was a song by that name but it was not in the studio release of the film), a past participle adjective formed from twitter in the "tremulous excitement" noun sense (1670s) + pate (n.2) "head" (compare flutterpated, 1894).
Thumper: Why are they acting that way?
Friend Owl: Why, don't you know? They're twitterpated.
Flower, Bambi, Thumper: Twitterpated?
Friend Owl: Yes. Nearly everybody gets twitterpated in the springtime. For example: You're walking along, minding your own business. You're looking neither to the left, nor to the right, when all of a sudden you run smack into a pretty face. Woo-woo! You begin to get weak in the knees. Your head's in a whirl. And then you feel light as a feather, and before you know it, you're walking on air. And then you know what? You're knocked for a loop, and you completely lose your head!
Thumper: Gosh, that's awful.
exit (n.): 1530s (late 15c. as a Latin word in English), originally a stage direction, from Latin exit "he or she goes out," third person singular present indicative of exire "go out, go forth, depart," from ex- "out" (see ex-) + ire "to go" (see ion). Also from Latin exitus "a leaving, a going out," noun of action from exire. Meaning "a departure" (originally from the stage) is from 1580s. Meaning "a way of departure" is from 1690s; specific meaning "door for leaving" is from 1786. The verb is c. 1600, from the noun; it ought to be left to stage directions and the clunky jargon of police reports. Related: Exited; exiting.
Those who neither know Latin nor read plays are apt to forget or not know that this is a singular verb with plural exeunt. [Fowler]
Exit poll attested by 1980.
Druid (n.): 1560s, from French druide, from Latin druidae (plural), from Gaulish Druides, from Celtic compound *dru-wid-, probably representing Old Celtic *derwos "true"/PIE *dru- "tree" (especially oak; see tree (n.)) + *wid- "to know" (see vision). Hence, literally, perhaps, "they who know the oak" (perhaps in allusion to divination from mistletoe). Anglo-Saxon, too, used identical words to mean "tree" and "truth" (treow).

The English form comes via Latin, not immediately from Celtic. The Old Irish form was drui (dative and accusative druid; plural druad); Modern Irish and Gaelic draoi, genitive druadh "magician, sorcerer." Not to be confused with United Ancient Order of Druids, secret benefit society founded in London 1781.
curious (adj.): mid-14c., "eager to know" (often in a bad sense), from Old French curios "solicitous, anxious, inquisitive; odd, strange" (Modern French curieux) and directly from Latin curiosus "careful, diligent; inquiring eagerly, meddlesome," akin to cura "care" (see cure (n.)). The objective sense of "exciting curiosity" is 1715 in English. In booksellers' catalogues, the word means "erotic, pornographic." Curiouser and curiouser is from "Alice in Wonderland" (1865).
half-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.
ignominious (adj.): early 15c., from Middle French *ignominieus or directly from Latin ignominiosus "disgraceful, shameful," from ignominia "disgrace, infamy, loss of a (good) name," from assimilated form of in- "not, opposite of" (see in- (1)) + nomen (genitive nominis) "name" (see name (n.)). The Latin spelling perhaps influenced by words from Old Latin gnoscere "come to know." Related: Ignominiously; ignominiousness.