Where did the word diet come from?

The word "diet" comes from the Old French word "diète", which itself came from the Latin word "diaeta".

"Diaeta" originally meant "way of life" or "manner of living", encompassing everything from food and drink to exercise and sleep habits.

Over time, the meaning of "diet" narrowed down to specifically refer to "food and drink", and eventually to "a regulated intake of food and drink", which is the meaning we use today.