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"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- "to give, allot." Often with a sense of restriction since 14c.; hence put (someone) on a diet (mid-15c.).
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.
diet di·et (dī'ĭt)
Food and drink in general.
A prescribed course of eating and drinking in which the amount and kind of food, as well as the times at which it is to be taken, are regulated for therapeutic purposes.
Reduction of caloric intake so as to lose weight.