facial hair vs sideburn

facial hair and sideburn both are nouns.

Word	Noun	Adjective	Verb	Adverb
facial hair	Yes	No	No	No
sideburn	Yes	No	No	No

As nouns, sideburn is a hyponym of facial hair; that is, sideburn is a word with a more specific, narrower meaning than facial hair:

facial hair: hair on the face (especially on the face of a man)
sideburn: facial hair that has grown down the side of a man's face in front of the ears (especially when the rest of the beard is shaved off)

Other hyponyms of facial hair include beard, face fungus, whiskers, moustache, mustache, burnside, mutton chop, side-whiskers.

facial hair (noun)	sideburn (noun)
hair on the face (especially on the face of a man)	facial hair that has grown down the side of a man's face in front of the ears (especially when the rest of the beard is shaved off)