Merriam-Webster Collegiate Dictionary - diet

 I. noun  Etymology: Middle English ~e, from Anglo-French, from Latin diaeta, from Greek diaita, literally, manner of living, from diaitasthai to lead one's life  Date: 13th century  1.  a. food and drink regularly provided or consumed  b. habitual nourishment  c. the kind and amount of food prescribed for a person or animal for a special reason  d. a regimen of eating and drinking sparingly so as to reduce one's weight going on a ~  2. something provided or experienced repeatedly a ~ of Broadway shows and nightclubs — Frederick Wyatt  II. verb  Date: 14th century  transitive verb  1. to cause to take food ; feed  2. to cause to eat and drink sparingly or according to prescribed rules  intransitive verb to eat sparingly or according to prescribed rules  • ~er noun  III. adjective  Date: 1963  1. reduced in calories a ~ soft drink  2. promoting weight loss (as by depressing appetite) ~ pills  IV. noun  Etymology: Middle English ~e day's journey, day set for a meeting, from Medieval Latin ~a, literally, daily regimen, ~ (taken as a derivative of Latin dies day), from Latin diaeta  Date: 1565  1. a formal deliberative assembly of princes or estates  2. any of various national or provincial legislatures DIETARILY  adverb see dietary II