nevus flammeus vs port-wine stain

nevus flammeus and port-wine stain both are nouns.

Word	Noun	Adjective	Verb	Adverb
nevus flammeus	Yes	No	No	No
port-wine stain	Yes	No	No	No

As nouns, nevus flammeus and port-wine stain are synonyms defined as:

nevus flammeus and port-wine stain: a flat birthmark varying from pink to purple

nevus flammeus (noun)	port-wine stain (noun)
a flat birthmark varying from pink to purple	a flat birthmark varying from pink to purple