Meaning

noun a prescribed selection of foods

noun a legislative assembly in certain countries (e.g., Japan)

noun the usual food and drink consumed by an organism (person or animal)

originFrom Middle English diet, dyet, from Old French diete, from Medieval Latin diēta, diaeta (“a public assembly; set day of trial; a day's journey”), from Ancient Greek δῐ́αιτα (dĭ́aita, “way of living, living space; decision, judgement”), influenced by Latin diēs (“day”).

Etymology from Wiktionary, CC BY-SA 3.0