membrane bone vs os

membrane bone and os both are nouns.

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

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

membrane bone: any bone that develops within membranous tissue without previous cartilage formation; e.g. the clavicle and bones of the skull
os: rigid connective tissue that makes up the skeleton of vertebrates

Other hypernyms of membrane bone include bone.

membrane bone (noun)	os (noun)
any bone that develops within membranous tissue without previous cartilage formation; e.g. the clavicle and bones of the skull	rigid connective tissue that makes up the skeleton of vertebrates
	a mouth or mouthlike opening