fishbone vs os

fishbone and os both are nouns.

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

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

Other hypernyms of fishbone include bone.

fishbone (noun)	os (noun)
a bone of a fish	rigid connective tissue that makes up the skeleton of vertebrates
	a mouth or mouthlike opening