fat person vs butterball

fat person and butterball both are nouns.

Word	Noun	Adjective	Verb	Adverb
fat person	Yes	No	No	No
butterball	Yes	No	No	No

As nouns, fat person and butterball are synonyms defined as:

Other synonyms of fat person include fatso, fatty, roly-poly.

fat person (noun)	butterball (noun)
a rotund individual	small North American diving duck; males have bushy head plumage
	a rotund individual