di·et 1 
(dīĭt)
(dīĭt)n.
1. The usual food and drink of a person or animal.
2. A regulated selection of foods, as for medical reasons or cosmetic weight loss.
3. Something used, enjoyed, or provided regularly: subsisted on a diet of detective novels during his vacation.
adj.
1. Of or relating to a food regimen designed to promote weight loss in a person or an animal: the diet industry.
2.
a. Having fewer calories.
b. Sweetened with a noncaloric sugar substitute.
3. Designed to reduce or suppress the appetite: diet pills; diet drugs.
v. di·et·ed, di·et·ing, di·ets
v.intr.
To eat and drink according to a regulated system, especially so as to lose weight or control a medical condition.
v.tr.
To regulate or prescribe food and drink for.
[Middle English diete, from Old French, from Latin diaeta, way of living, diet, from Greek diaita, back-formation from diaitāsthai, to live one's life, middle voice of diaitān, to treat.]
diet·er n.