diet [noun] - the usual food and drink of a person or animal.
Example: My diet is very healthy; lots of vegatables and fat free food.
diet [noun] - a regulated selection of foods, as for medical reasons or cosmetic weight loss.
Example: The doctor put her on a strict diet in order to reduce her weight.
Example: I'm going to start a new diet next week.
diet [noun] - something used, enjoyed, or provided regularly.
Example: I lived on a daily diet of coffee and cigarettes for many years.
diet [verb] - to eat and drink according to a regulated system, especially to lose weight or control a medical condition.
Example: She has been dieting for 3 months now so as to lose weight.