diet >> /ˈdaɪət/
Definition: [noun] The kinds of food that a person, animal, or community habitually eats.
Example: a vegetarian diet
Definition: [noun] A special course of food to which one restricts oneself, either to lose weight or for medical reasons.
Example: I'm going on a diet
Definition: [intransitive verb] Restrict oneself to small amounts or special kinds of food in order to lose weight.
Example: it's difficult to diet