dieter vs doer

dieter and doer both are nouns.

Word	Noun	Adjective	Verb	Adverb
dieter	Yes	No	No	No
doer	Yes	No	No	No

As nouns, doer is a hypernym of dieter; that is, doer is a word with a broader meaning than dieter:

Other hypernyms of dieter include actor, worker.

dieter (noun)	doer (noun)
a person who diets	a person who acts and gets things done