haircut vs flattop

haircut and flattop both are nouns.

Word	Noun	Adjective	Verb	Adverb
haircut	Yes	No	No	No
flattop	Yes	No	No	No

As nouns, flattop is a hyponym of haircut; that is, flattop is a word with a more specific, narrower meaning than haircut:

Other hyponyms of haircut include brush cut, butch, crew cut, mohawk, mohawk haircut.

haircut (noun)	flattop (noun)
the act of cutting the hair	a large warship that carries planes and has a long flat deck for takeoffs and landings
the style in which hair has been cut	a closely cropped haircut; usually for men or boys