metacarpal vs os

metacarpal and os both are nouns.

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

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

Other hypernyms of metacarpal include bone.

metacarpal (noun)	os (noun)
any bone of the hand between the wrist and fingers	rigid connective tissue that makes up the skeleton of vertebrates
	a mouth or mouthlike opening

metacarpal (adjective)	os (adjective)
of or relating to the metacarpus