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.
didgeridoo (n.) Look up didgeridoo at Dictionary.com
1924, Australian, of imitative origin.
didn't Look up didn't at Dictionary.com
by 1775, contraction of did not.
dido (n.) Look up dido at Dictionary.com
"prank, caper," 1807, American English slang, perhaps from the name of the Carthaginian queen in the "Aeneid." Usually in phrase to cut didoes.
didst Look up didst at Dictionary.com
archaic 2nd person singular past indicative of do (q.v.).
die (v.) Look up die at Dictionary.com
mid-12c., possibly from Old Danish døja or Old Norse deyja "to die, pass away," both from Proto-Germanic *dawjan (cognates: Old Frisian deja "to kill," Old Saxon doian, Old High German touwen, Gothic diwans "mortal"), from PIE root *dheu- (3) "to pass away, die, become senseless" (cognates: Old Irish dith "end, death," Old Church Slavonic daviti, Russian davit' "to choke, suffer").

It has been speculated that Old English had *diegan, from the same source, but it is not in any of the surviving texts and the preferred words were steorfan (see starve), sweltan (see swelter), wesan dead, also forðgan and other euphemisms.

Languages usually don't borrow words from abroad for central life experiences, but "die" words are an exception, because they are often hidden or changed euphemistically out of superstitious dread. A Dutch euphemism translates as "to give the pipe to Maarten." Regularly spelled dege through 15c., and still pronounced "dee" by some in Lancashire and Scotland. Used figuratively (of sounds, etc.) from 1580s. Related: Died; dies.
die (n.) Look up die at Dictionary.com
early 14c. (as a plural, late 14c. as a singular), from Old French de "die, dice," of uncertain origin. Common Romanic (cognates: Spanish, Portuguese, Italian dado, Provençal dat, Catalan dau), perhaps from Latin datum "given," past participle of dare (see date (n.1)), which, in addition to "give," had a secondary sense of "to play" (as a chess piece); or else from "what is given" (by chance or Fortune). Sense of "stamping block or tool" first recorded 1690s.
diehard Look up diehard at Dictionary.com
also die-hard, 1844 (n.), in reference to the 57th Regiment of Foot in the British Army; as an adjective, attested from 1871; from die (v.) + hard (adv.). As a brand name of an automobile battery, DieHard, introduced by Sears in 1967.
dieresis (n.) Look up dieresis at Dictionary.com
also diaeresis, 1610s, "sign marking the division of a diphthong into two simple sounds," from Late Latin diaeresis, from Greek diairesis "division," noun of action from diairein "to divide, separate," from dia- "apart" (see dia-) + hairein "to take" (see heresy). In classical prosody, "the slight break in the forward motion of a line that is felt when the end of a foot coincides with the end of a word" [Miller Williams, "Patterns of Poetry"].
Dies Irae Look up Dies Irae at Dictionary.com
literally "day of wrath," first words of Latin hymn of Last Judgment, attributed to Thomas of Celano (c.1250). See diurnal + ire.
diesel (adj.) Look up diesel at Dictionary.com
1894, named for Rudolf Diesel (1858-1913), German mechanical engineer who designed this type of engine.
diet (n.1) Look up diet at Dictionary.com
"regular food," early 13c., from Old French diete (13c.) "diet, pittance, fare," from Medieval Latin dieta "parliamentary assembly," also "a day's work, diet, daily food allowance," from Latin diaeta "prescribed way of life," from Greek diaita, originally "way of life, regimen, dwelling," related to diaitasthai "lead one's life," and from diaitan, originally "separate, select" (food and drink), frequentative of *diainysthai "take apart," from dia- "apart" + ainysthai "take," from PIE root *ai- (1) "to give, allot." Often with a sense of restriction since 14c.; hence put (someone) on a diet (mid-15c.).
diet (n.2) Look up diet at Dictionary.com
"assembly," mid-15c., from Medieval Latin dieta, variant of diaeta "daily office (of the Church), daily duty, assembly, meeting of counselors," from Greek diaita (see diet (n.1)), but associated with Latin dies "day" (see diurnal).
diet (v.) Look up diet at Dictionary.com
late 14c., "to regulate one's diet for the sake of health," from Old French dieter, from diete (see diet (n.1)); meaning "to regulate oneself as to food" (especially against fatness) is from 1650s. Related: Dieted; dieting. An obsolete word for this is banting. The adjective in this sense (Diet Coke, etc.) is from 1963, originally American English.
dietary (adj.) Look up dietary at Dictionary.com
1610s, from Medieval Latin dietarius, from Latin diaetarius, from diaeta (see diet (n.1)).
dietetic (adj.) Look up dietetic at Dictionary.com
1570s, from Latin diaeteticus, from Greek diaitetikos "of or pertaining to diet," from diaita (see diet (1)). As a noun from 1759.
dietetics (n.) Look up dietetics at Dictionary.com
1540s, see dietetic + -ics.
dietician (n.) Look up dietician at Dictionary.com
1845, from diet (n.1) on model of physician. Earlier was dietist (c.1600).
dietitian (n.) Look up dietitian at Dictionary.com
see dietician.
Dietrich Look up Dietrich at Dictionary.com
German masc. name and surname, literally "folk-rule" (Dutch Diederik), from Old High German Theodric, from theuda "folk, people" (see Teutonic) + rihhi "rule" (see Reich). Variants or familiar forms include Derrick, Dierks, Dieter, Dirk. Compare Theodoric.
differ (v.) Look up differ at Dictionary.com
late 14c., from Old French differer (14c.) and directly from Latin differre "to set apart, differ," from dis- "away from" (see dis-) + ferre "carry" (see infer).

Two senses that were present in Latin have gone separate ways in English since c.1500 with defer (transitive) and differ (intransitive). Related: Differed; differing.
difference (n.) Look up difference at Dictionary.com
mid-14c., from Old French difference (12c.) "difference, distinction; argument, dispute," from Latin differentia "diversity, difference," from differentem (nominative differens), present participle of differre "to set apart" (see differ). Sense of "a quarrel" first attested late 14c. Colloquial phrase what's the diff? first recorded 1896.
different (adj.) Look up different at Dictionary.com
late 14c., from Old French different (14c.), from Latin differentem (nominative differens) "differing, different," present participle of differre "to set apart" (see differ). Colloquial sense of "special" attested by 1912. Related: Differently.
differential (adj.) Look up differential at Dictionary.com
1640s, from Medieval Latin differentialis, from Latin differentia (see difference). Related: Differentially.
differentiate (v.) Look up differentiate at Dictionary.com
1816, from Medieval Latin differentiatus, past participle of differentiare, from Latin differentia (see difference).

Originally a mathematical term; transitive and non-technical sense of "discriminate between" is from 1876. Earlier, difference had been used as a verb in this sense. Related: Differentiated; differentiating; differentiation.
difficult (adj.) Look up difficult at Dictionary.com
c.1400, apparently a back-formation from difficulty. French has difficile, Latin difficilis. Of persons, "hard to please," from 1580s.
difficulty (n.) Look up difficulty at Dictionary.com
late 14c., from Old French difficulté, from Latin difficultatem (nominative difficultas) "difficulty, distress, poverty," from difficilis "hard," from dis- "not, away from" (see dis-) + facilis "easy" (see facile).
diffidence (n.) Look up diffidence at Dictionary.com
c.1400, from Latin diffidentia "mistrust, distrust, want of confidence," from diffidere "to mistrust, lack confidence," from dis- "away" (see dis-) + fidere "to trust" (see faith). Modern sense is of "distrusting oneself" (1650s). The original sense was the opposite of confidence.
diffident (adj.) Look up diffident at Dictionary.com
mid-15c., from Latin diffidentem (nominative diffidens), present participle of diffidere (see diffidence). Related: Diffidently.
diffract (v.) Look up diffract at Dictionary.com
1803, perhaps a back-formation from diffraction. Related: Diffracted; diffracting.
diffraction (n.) Look up diffraction at Dictionary.com
1670s, from French diffraction (17c.) or directly from Modern Latin diffractionem (nominative diffractio), noun of action from past participle stem of Latin diffringere "break in pieces," from dis- "apart" (see dis-) + frangere "to break" (see fraction).
diffuse (v.) Look up diffuse at Dictionary.com
1520s (transitive), 1650s (intransitive), from Latin diffusus, past participle of diffundere "to pour out or away" (see diffusion). Related: Diffused; diffusing.
diffuse (adj.) Look up diffuse at Dictionary.com
early 15c., from Latin diffusus (see diffuse (v.)).
diffusion (n.) Look up diffusion at Dictionary.com
late 14c., from Latin diffusionem (nominative diffusio) "a pouring forth," noun of action from past participle stem of diffundere "scatter, pour out," from dis- "apart, in every direction" (see dis-) + fundere "pour" (see found (v.2)).
dig (v.) Look up dig at Dictionary.com
early 14c. (diggen), of uncertain origin, perhaps related to dike and ditch, either via Old French diguer (ultimately from a Germanic source), or directly from an unrecorded Old English word. Native words were deolfan (see delve), grafan (see grave (v.)).

Slang sense of "understand" first recorded 1934 in Black English, probably based on the notion of "excavate." A slightly varied sense of "appreciate" emerged 1939. Strong past participle dug appeared 16c., but is not etymological. Related: Digging.
dig (n.) Look up dig at Dictionary.com
late 17c. as "a tool for digging," from dig (v.). Meaning "archaeological expedition" is from 1896. Meaning "thrust or poke" (as with an elbow) is from 1819; figurative sense of this is from 1840.
digamist (n.) Look up digamist at Dictionary.com
"person who has married a second time," 1650s, from di- (1) + -gamy + -ist.
digest (n.) Look up digest at Dictionary.com
"collection of writing," late 14c., from Latin digesta, from neuter plural of digestus, literally "digested thing," noun use of past participle of digerere "to separate, divide, arrange," from dis- "apart" (see dis-) + gerere "to carry" (see gest).
digest (v.) Look up digest at Dictionary.com
"assimilate food in bowels," late 14c., from Latin digestus (see digest (n.)). Related: Digested; digesting.
digestible (adj.) Look up digestible at Dictionary.com
late 14c., from Old French digestible, from Latin digestibilis, from past participle stem of digerere (see digest (n.)).
digestion (n.) Look up digestion at Dictionary.com
late 14c., from Old French digestion (13c.), from Latin digestionem (nominative digestio), noun of action from past participle stem of digerere (see digest (n.)).
digestive (n.) Look up digestive at Dictionary.com
late 14c., from Old French digestif (14c.), from Late Latin digestivus "pertaining to digestion," from past participle stem of Latin digerere (see digest (n.)). From 1530s as an adjective. The noun in the French form digestif is attested from 1908.
digger (n.) Look up digger at Dictionary.com
mid-15c., "one who digs," agent noun from dig (v.). The communistic movement in England so called from 1649.
dight (v.) Look up dight at Dictionary.com
"to adorn" (archaic or poetic), Old English dihtan "dictate, appoint, ordain; guide; compose," an early borrowing from Latin dictare "to dictate" (see dictate (v.)).

The Latin word borrowed even earlier into continental Germanic became Old High German dihton "to write compose," German dichten "to write poetry." In Middle English, dight exploded to a vast array of meanings (including "to rule," "to handle," "to abuse," "to have sex with," "to kill," "to clothe," "to make ready," "to repair") till it was one of the most-used verbs in the language, but all senses have faded now into obscurity, dialect, or poetic use.
digit (n.) Look up digit at Dictionary.com
late 14c., "numeral below 10," from Latin digitus "finger or toe" (also with secondary meanings dealing in counting and numerals), related to dicere "tell, say, point out" (see diction). Numerical sense is because numerals under 10 were counted on fingers. The "finger or toe" sense in English is attested from 1640s.
digital (adj.) Look up digital at Dictionary.com
1650s, "pertaining to fingers," from Latin digitalis, from digitus (see digit). Meaning "using numerical digits" is from 1938, especially of computers after c.1945; in reference to recording or broadcasting, from 1960. Related: Digitize.
digitalis (n.) Look up digitalis at Dictionary.com
1660s, Modern Latin translation of German fingerhut, the German name of "foxglove," literally "thimble." Named by Fuchs (1542), and so called for its shape. The medicine (originally extracted from the plant) is so called from 1799.
dignified (adj.) Look up dignified at Dictionary.com
past participle adjective from dignify; 1660s in sense "ranking as a dignitary;" 1812 in sense "having a dignified manner."