diametric (adj.) Look up diametric at Dictionary.com
1802, probably shortened from diametrical (1550s); see diameter + -ical.
diametrically (adv.) Look up diametrically at Dictionary.com
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.) Look up diamond at Dictionary.com
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 Look up Diana at Dictionary.com
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.) Look up dianetics at Dictionary.com
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.) Look up Dianthus at Dictionary.com
1849, from Modern Latin (Linnaeus), literally "flower of Zeus," from Greek Dios, genitive of Zeus "Zeus" (see Zeus) + anthos "flower" (see anther).
diaper (n.) Look up diaper at Dictionary.com
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.) Look up diaper at Dictionary.com
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.) Look up diaphanous at Dictionary.com
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.) Look up diaphragm at Dictionary.com
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.) Look up diarist at Dictionary.com
1818; see diary + -ist.
diarize (v.) Look up diarize at Dictionary.com
1842; see diary + -ize. Related: Diarized; diarizing.
diarrhea (n.) Look up diarrhea at Dictionary.com
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 Look up diarrhoea at Dictionary.com
variant spelling of diarrhea (q.v.); see also oe.
diary (n.) Look up diary at Dictionary.com
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.) Look up diaspora at Dictionary.com
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.) Look up diastase at Dictionary.com
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.) Look up diastole at Dictionary.com
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.) Look up diatessaron at Dictionary.com
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.) Look up diatom at Dictionary.com
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.) Look up diatonic at Dictionary.com
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.) Look up diatribe at Dictionary.com
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.) Look up Diazepam at Dictionary.com
1961, from (benzo)diazep(ine) + -am, apparently an arbitrary suffix. The element diazo- denotes two nitrogen atoms combined with one hydrocarbon radical.
dib Look up dib at Dictionary.com
see dibs.
dibble (n.) Look up dibble at Dictionary.com
"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.) Look up dibs at Dictionary.com
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.) Look up dice at Dictionary.com
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.) Look up dice at Dictionary.com
"to cut into cubes," late 14c., from dice (n.). Meaning "to play at dice" is from early 15c. Related: Diced; dicing.
dicey (adj.) Look up dicey at Dictionary.com
"risky, uncertain" (as the roll of dice), 1940s, aviators' jargon, from dice (n.) + -y (2). Related: Diciness.
dichotomy (n.) Look up dichotomy at Dictionary.com
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.) Look up dick at Dictionary.com
"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 Look up Dick Whittington at Dictionary.com
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 Look up dickens at Dictionary.com
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.) Look up dicker at Dictionary.com
"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.) Look up dickhead at Dictionary.com
"stupid, contemptible person," by 1969, from dick in the "penis" sense + head.
dicky (n.) Look up dicky at Dictionary.com
"detached shirt front," 1811; "a small bird," 1851; diminutive of dick, but the applications are obscure in both cases.
Dictaphone (n.) Look up Dictaphone at Dictionary.com
trademarked by the Columbia Graphophone Company in 1907; from dictation + -phone. A separate company from 1923.
dictate (v.) Look up dictate at Dictionary.com
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.) Look up dictate at Dictionary.com
1590s, from Latin dictatum "something dictated," noun use of neuter past participle of dictare (see dictate (v.)).
dictation (n.) Look up dictation at Dictionary.com
1650s, from Late Latin dictationem (nominative dictatio), noun of action from past participle stem of dictare (see dictate (v.)).
dictator (n.) Look up dictator at Dictionary.com
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.) Look up dictatorial at Dictionary.com
1701; see dictator + -ial. Related: Dictatorially.
dictatorship (n.) Look up dictatorship at Dictionary.com
1580s, from dictator + -ship.
diction (n.) Look up diction at Dictionary.com
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.) Look up dictionary at Dictionary.com
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 Look up Dictograph at Dictionary.com
patented 1907 in U.S. by K.M. Turner and W. Donnan, from dictation + -graph "instrument for recording; something written."
dictum (n.) Look up dictum at Dictionary.com
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.) Look up did at Dictionary.com
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.) Look up didactic at Dictionary.com
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.) Look up diddle at Dictionary.com
"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.