nevus vs nevus flammeus

nevus and nevus flammeus both are nouns.

Word	Noun	Adjective	Verb	Adverb
nevus	Yes	No	No	No
nevus flammeus	Yes	No	No	No

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

Other hyponyms of nevus include port-wine stain, hemangioma simplex, strawberry, strawberry mark.

nevus (noun)	nevus flammeus (noun)
a blemish on the skin that is formed before birth	a flat birthmark varying from pink to purple