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diet (n.1)[diet 词源字典]: "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 etymology, diet origin, 英语词源]
diet (n.2): "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.): 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.): 1610s, from Medieval Latin dietarius, from Latin diaetarius, from diaeta (see diet (n.1)).
dietetic (adj.): 1570s, from Latin diaeteticus, from Greek diaitetikos "of or pertaining to diet," from diaita (see diet (1)). As a noun from 1759.
dietetics (n.): 1540s, see dietetic + -ics.
dietician (n.): 1845, from diet (n.1) on model of physician. Earlier was dietist (c. 1600).
dietitian (n.): see dietician.
Dietrich: 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. Theodric the Ostrogoth, who held sway in Italy 493-526, appears in later German tales as Dietrich von Bern (Verona).
differ (v.): 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.): 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.): 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.): 1640s, from Medieval Latin differentialis, from Latin differentia (see difference). Related: Differentially.
differentiate (v.): 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.): c. 1400, apparently a back-formation from difficulty. French has difficile, Latin difficilis. Of persons, "hard to please," from 1580s.
difficulty (n.): 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.): 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.): mid-15c., from Latin diffidentem (nominative diffidens), present participle of diffidere (see diffidence). Related: Diffidently.
diffract (v.): 1803, perhaps a back-formation from diffraction. Related: Diffracted; diffracting.
diffraction (n.): 1670s, from French diffraction (17c.) or directly from Modern Latin diffractionem (nominative diffractio), noun of action from past participle stem of Latin diffringere "break apart in pieces," from dis- "apart" (see dis-) + frangere "to break" (see fraction).