sphenoid bone vs os

sphenoid bone and os both are nouns.

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

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

Other hypernyms of sphenoid bone include bone.

sphenoid bone (noun)	os (noun)
butterfly-shaped bone at the base of the skull	rigid connective tissue that makes up the skeleton of vertebrates
	a mouth or mouthlike opening