calvaria vs os

calvaria and os both are nouns.

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

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

Other hypernyms of calvaria include bone.

calvaria (noun)	os (noun)
the dome of the skull	rigid connective tissue that makes up the skeleton of vertebrates
	a mouth or mouthlike opening