metatarsal vs os

metatarsal and os both are nouns.

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

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

Other hypernyms of metatarsal include bone.

metatarsal (noun)	os (noun)
any bone of the foot between the ankle and the toes	rigid connective tissue that makes up the skeleton of vertebrates
	a mouth or mouthlike opening

metatarsal (adjective)	os (adjective)
of or relating to the metatarsus