Online Etymology Dictionary

diametric (adj.): 1802, probably shortened from diametrical (1550s); see diameter + -ical.
diametrically (adv.): 1630s, "completely" (opposed, contrary, etc.); see diametric. Mostly in figurative use; the two points that mark the ends of a line of diameter across a circle are opposite one another.
diamond (n.): early 14c., from Old French diamant, from Medieval Latin diamantem (nominative diamas), from Vulgar Latin *adiamantem (altered by influence of the many Greek words in dia-), from Latin adamantem (nominative adamans) "the hardest metal," later, "diamond" (see adamant). Playing card suit is from 1590s; Sense in baseball is American English, 1875.
Diana: c. 1200, ancient Italian goddess of the moon, patroness of virginity and hunting, later identified with Greek Artemis, and through her with eastern goddesses such as Diana of Ephesus. The name is explained as *Diwjana, from *diw-yo-, from PIE root *dyeu- "to shine" (see Zeus) in reference to the shining moon, or from dius "godly."
dianetics (n.): 1950, coined by U.S. writer L. Ron Hubbard (1911-1986), an alteration of dianoetic (1670s) "of or pertaining to thought," from Greek dianoetikos "of or for thinking; intellectual," from dianoetos, verbal adjective from dianoe-esthai "to think," from dia- "through" (see dia-) + noe-ein "to think, suppose."
Dianthus (n.): 1849, from Modern Latin (Linnaeus), literally "flower of Zeus," from Greek Dios, genitive of Zeus "Zeus" (see Zeus) + anthos "flower" (see anther).
diaper (n.): mid-14c., "fabric with a repeated pattern of figures," from Old French diaspre "ornamental cloth; flowered, patterned silk cloth," perhaps via Medieval Latin diasprum from Medieval Greek diaspros "thoroughly white," or perhaps "white interspersed with other colors," from dia- (see dia-) + aspros "white."

Aspros originally meant "rough," and was applied to the raised parts of coins (among other things), and thus was used in Byzantine Greek to mean "silver coin," from which the bright, shiny qualities made it an adjective for whiteness. Modern sense of "underpants for babies" is continuous since 1837, but such usage has been traced back to 1590s.
diaper (v.): late 14c., "to put a small, repeated pattern on," from Old French diaprer, variant of diasprer, from diaspre (see diaper (n.)). Meaning "to put a diaper on" (a baby) is attested by 1951. Related: Diapered; diapering.
diaphanous (adj.): 1610s, from Medieval Latin diaphanus, from Greek diaphanes "transparent," from dia- "through" (see dia-) + phainesthai, middle voice form (subject acting on itself) of phainein "to show" (see phantasm).
diaphragm (n.): late 14c., from Late Latin diaphragma, from Greek diaphragma "partition, barrier, muscle which divides the thorax from the abdomen," from diaphrassein "to barricade," from dia- "across" (see dia-) + phrassein "to fence or hedge in." The native word is midriff. Meaning "contraceptive cap" is from 1933.
diarist (n.): 1818; see diary + -ist.
diarize (v.): 1842; see diary + -ize. Related: Diarized; diarizing.
diarrhea (n.): late 14c., from Old French diarrie, from Late Latin diarrhoea, from Greek diarrhoia "diarrhea" (coined by Hippocrates), literally "a flowing through," from diarrhein "to flow through," from dia- "through" (see dia-) + rhein "to flow" (see rheum). Respelled 16c. from diarria on Latin model.
diarrhoea: variant spelling of diarrhea (q.v.); see also oe.
diary (n.): 1580s, from Latin diarium "daily allowance," later "a journal," neuter of diarius "daily," from dies "day" (see diurnal); also see -ary. Earliest sense was a daily record of events; sense of the book in which such are written is said to be first attested in Ben Jonson's "Volpone" (1605).
diaspora (n.): 1876, from Greek diaspora "dispersion," from diaspeirein "to scatter about, disperse," from dia- "about, across" (see dia-) + speirein "to scatter" (see sprout). The Greek word was used in Septuagint in Deut. xxviii:25. A Hebrew word for it is galuth "exile." Related: Diasporic.
diastase (n.): enzyme or group of enzymes found in a seed and capable of converting starch into sugar, coined 1833 by Payen and Persoz from Greek diastasis "a setting apart," from dia- "across" (see dia-) + stasis "a standing" (see stasis).
diastole (n.): 1570s, from medical Latin diastole, from Greek diastole "drawing asunder, dilation," from diastellein, from dia- "through, thoroughly, entirely" (see dia-) + stellein "to set in order, arrange, array, equip, make ready," from PIE *stel-yo-, suffixed form of root *stel- "to put, stand," with derivatives referring to a standing object or place (see stall (n.1)).
diatessaron (n.): late 14c. as a term in music meaning "interval of a fourth;" 1803 in reference to harmonizings of the gospels, especially that of Tatian (2c.), from Greek dia tessaron, from dia "composed of" (literally "through;" see dia-) + tessaron "four," related to tessares (see four).
diatom (n.): 1845, coined from Greek diatomos "cut in two," from diatemnein "to cut through," from dia- "through" (see dia-) + temnein "to cut" (see tome). So called because they typically appear to have been cut in half. Related: Diatomic.
diatonic (adj.): c. 1600, from French diatonique, from Latin diatonicus, from Greek diatonikos, from diatonos "extending; pertaining to the diatonic scale," from dia- (see dia-) + teinein "to stretch" (see tenet).
diatribe (n.): 1640s (in Latin form in English from 1580s), "discourse, critical dissertation," from French diatribe (15c.), from Latin diatriba "learned discussion," from Greek diatribe "employment, study," in Plato, "discourse," literally "a wearing away (of time)," from dia- "away" (see dia-) + tribein "to wear, rub," from PIE root *tere- (1) "to rub, turn, twist" (see throw (v.)). Sense of "invective" is 1804, apparently from French.
Diazepam (n.): 1961, from (benzo)diazep(ine) + -am, apparently an arbitrary suffix. The element diazo- denotes two nitrogen atoms combined with one hydrocarbon radical.
dib: see dibs.
dibble (n.): "tool to make a hole in the soil (as to plant seeds)," mid-15c., probably from Middle English dibben (perhaps akin to dip) + instrumental suffix -el (1). The verb is from 1580s. Related: Dibbled; dibbling.
dibs (interj.): children's word to express a claim on something, 1915, originally U.S., apparently from earlier senses "a portion or share" and "money" (early 19c. colloquial), probably a contraction of dibstone "a knucklebone or jack in a children's game" (1690s), in which the first element is of unknown origin.
dice (n.): early 14c., des, dys, plural of dy (see die (n.)), altered 14c. to dyse, dyce, and 15c. to dice. "As in pence, the plural s retains its original breath sound, probably because these words were not felt as ordinary plurals, but as collective words" [OED]. Sometimes used as singular 1400-1700.
dice (v.): "to cut into cubes," late 14c., from dice (n.). Meaning "to play at dice" is from early 15c. Related: Diced; dicing.
dicey (adj.): "risky, uncertain" (as the roll of dice), 1940s, aviators' jargon, from dice (n.) + -y (2). Related: Diciness.
dichotomy (n.): c. 1600, from Greek dichotomia "a cutting in half," from dicha "in two, asunder" (related to dis "twice") + temnein "to cut" (see tome).
dick (n.): "fellow, lad, man," 1550s, rhyming nickname for Rick, short for Richard, one of the commonest English names, it has long been a synonym for "fellow," and so most of the slang senses are probably very old, but naturally hard to find in the surviving records. The meaning "penis" is attested from 1891 in Farmer's slang dictionary (possibly British army slang). Meaning "detective" is recorded from 1908, perhaps as a shortened variant of detective.
Dick Whittington: The story is an old one, told under other names throughout Europe, of a poor boy who sends a cat he had bought for a penny as his stake in a trading voyage; the captain sells it on his behalf for a fortune to a foreign king whose palace is overrun by rats. The hero devotes part of his windfall to charity, which may be why the legend attached in England since 16c. to Sir Richard Whittington (d.1423), three times Lord Mayor of London, who died childless and devoted large sums in his will to churches, almshouses, and St. Bartholomew's Hospital.
dickens: exclamation, 1590s, apparently a substitute for devil; probably altered from Dickon, nickname for Richard and source of the surnames Dickens and Dickenson, but exact derivation and meaning are unknown.
dicker (v.): "haggle, bargain in a petty way," 1802, American English, perhaps from dicker (n.) "a unit or package of tens," especially hides (attested from late 13c.), perhaps from Latin decuria "parcel of ten" (supposedly a unit of barter on the Roman frontier; compare German Decher "set of ten things"), from decem "ten" (see ten) on model of centuria from centum.
dickhead (n.): "stupid, contemptible person," by 1969, from dick in the "penis" sense + head.
dicky (n.): "detached shirt front," 1811; "a small bird," 1851; diminutive of dick, but the applications are obscure in both cases.
Dictaphone (n.): trademarked by the Columbia Graphophone Company in 1907; from dictation + -phone. A separate company from 1923.
dictate (v.): 1590s, "to practice dictation, say aloud for another to write down," from Latin dictatus, past participle of dictare "say often, prescribe," frequentative of dicere "to say, speak" (see diction). Sense of "to command" is 1620s. Related: Dictated; dictates; dictating.
dictate (n.): 1590s, from Latin dictatum "something dictated," noun use of neuter past participle of dictare (see dictate (v.)).
dictation (n.): 1650s, from Late Latin dictationem (nominative dictatio), noun of action from past participle stem of dictare (see dictate (v.)).
dictator (n.): late 14c., from Latin dictator, agent noun from dictare (see dictate (v.)). Transferred sense of "one who has absolute power or authority" in any sphere is from c. 1600. In Latin use, a dictator was a judge in the Roman republic temporarily invested with absolute power.
dictatorial (adj.): 1701; see dictator + -ial. Related: Dictatorially.
dictatorship (n.): 1580s, from dictator + -ship.
diction (n.): 1540s, "a word;" 1580s, "expression of ideas in words," from Late Latin dictionem (nominative dictio) "a saying, expression, word," noun of action from dic-, past participle stem of Latin dicere "speak, tell, say" (source of French dire "to say"), related to dicare "proclaim, dedicate," from PIE root *deik- "to point out" (source also of Sanskrit dic- "point out, show," Greek deiknynai "to show, to prove," Latin digitus "finger," Old High German zeigon, German zeigen "to show," Old English teon "to accuse," tæcan "to teach").

Another cognate is Greek dike "custom, usage," and, via the notion of "right as dependent on custom," "law, a right; a judgment; a lawsuit, court case, trial; penalty awarded by a judge."
dictionary (n.): 1520s, from Medieval Latin dictionarium "collection of words and phrases," from Latin dictionarius "of words," from dictio "word" (see diction). Probably first English use in title of a book was in Sir Thomas Elyot's "Latin Dictionary" (1538) though Latin Dictionarius was so used from early 13c. Grose's 1788 "Dictionary of the Vulgar Tongue" has "RICHARD SNARY. A dictionary."
DICTIONARY, n. A malevolent literary device for cramping the growth of a language and making it hard and inelastic. This dictionary, however, is a most useful work. [Bierce]
Dictograph: patented 1907 in U.S. by K.M. Turner and W. Donnan, from dictation + -graph "instrument for recording; something written."
dictum (n.): 1660s, from Latin dictum "thing said (a saying, bon-mot, prophecy, etc.), an order, command," neuter of dictus, past participle of dicere "to say, speak" (see diction). In legal use, a judge's expression of opinion which is not the formal resolution of a case.
did (v.): Old English dyde, past tense of do (v.). The only remainder in Germanic of the old linguistic pattern of forming a past tense by reduplication of the stem of the present tense. Far back in Germanic the equivalent of did was used as a suffix to make the past tenses of other verbs, hence the English -ed suffix (Old English -de).
didactic (adj.): 1650s, from French didactique, from Greek didaktikos "apt at teaching," from didaktos "taught," past participle of didaskein "teach," from PIE root *dens- "wisdom, to teach, learn." Related: Didactically; didacticism.
diddle (v.): "to cheat, swindle," 1806, from dialectal duddle, diddle "to totter" (1630s). Meaning "waste time" is recorded from 1825. Meaning "to have sex with" is from 1879; that of "to masturbate" (especially of women) is from 1950s. More or less unrelated meanings that have gathered around a suggestive sound. Related: Diddled; diddling.