innominate bone vs os

innominate bone and os both are nouns.

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

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

innominate bone: large flaring bone forming one half of the pelvis; made up of the ilium and ischium and pubis
os: rigid connective tissue that makes up the skeleton of vertebrates

Other hypernyms of innominate bone include bone.

innominate bone (noun)	os (noun)
large flaring bone forming one half of the pelvis; made up of the ilium and ischium and pubis	rigid connective tissue that makes up the skeleton of vertebrates
	a mouth or mouthlike opening