flattop vs crew cut

flattop and crew cut both are nouns.

Word	Noun	Adjective	Verb	Adverb
flattop	Yes	No	No	No
crew cut	Yes	No	No	No

As nouns, flattop and crew cut are synonyms defined as:

flattop and crew cut: a closely cropped haircut; usually for men or boys

Other synonyms of flattop include butch.

flattop (noun)	crew cut (noun)
a large warship that carries planes and has a long flat deck for takeoffs and landings	a closely cropped haircut; usually for men or boys
a closely cropped haircut; usually for men or boys