dietetical vs diet

dietetical is not a noun while diet is a noun.

Word	Noun	Adjective	Verb	Adverb
dietetical	No	Yes	No	No
diet	Yes	No	Yes	No

dietetical (noun)	diet (noun)
	the act of restricting your food intake (or your intake of particular foods)
	a prescribed selection of foods
	the usual food and drink consumed by an organism (person or animal)
	a legislative assembly in certain countries (e.g., Japan)

dietetical (adjective)	diet (adjective)
of or relating to the diet

dietetical (verb)	diet (verb)
	eat sparingly, for health reasons or to lose weight
	follow a regimen or a diet, as for health reasons