cuboid bone vs os

cuboid bone and os both are nouns.

Word	Noun	Adjective	Verb	Adverb
cuboid bone	Yes	No	No	No
os	Yes	No	No	No

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

Other hypernyms of cuboid bone include bone.

cuboid bone (noun)	os (noun)
the cube shaped bone on the outer side of the tarsus	rigid connective tissue that makes up the skeleton of vertebrates
	a mouth or mouthlike opening