cheekbone vs os

cheekbone and os both are nouns.

Word	Noun	Adjective	Verb	Adverb
cheekbone	Yes	No	No	No
os	Yes	No	No	No

As nouns, os is a hypernym of cheekbone; that is, os is a word with a broader meaning than cheekbone:

cheekbone: the arch of bone beneath the eye that forms the prominence of the cheek
os: rigid connective tissue that makes up the skeleton of vertebrates

Other hypernyms of cheekbone include bone.

cheekbone (noun)	os (noun)
the arch of bone beneath the eye that forms the prominence of the cheek	rigid connective tissue that makes up the skeleton of vertebrates
	a mouth or mouthlike opening