butterball vs bufflehead

butterball and bufflehead both are nouns.

Word	Noun	Adjective	Verb	Adverb
butterball	Yes	No	No	No
bufflehead	Yes	No	No	No

As nouns, butterball and bufflehead are synonyms defined as:

butterball and bufflehead: small North American diving duck; males have bushy head plumage

Other synonyms of butterball include Bucephela albeola, dipper.

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