pubic bone vs os

pubic bone and os both are nouns.

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

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

pubic bone: one of the three sections of the hipbone; together these two bones form the front of the pelvis
os: rigid connective tissue that makes up the skeleton of vertebrates

Other hypernyms of pubic bone include bone.

pubic bone (noun)	os (noun)
one of the three sections of the hipbone; together these two bones form the front of the pelvis	rigid connective tissue that makes up the skeleton of vertebrates
	a mouth or mouthlike opening