pubis vs os pubis

pubis and os pubis both are nouns.

Word	Noun	Adjective	Verb	Adverb
pubis	Yes	No	No	No
os pubis	Yes	No	No	No

As nouns, pubis and os pubis are synonyms defined as:

pubis and os pubis: one of the three sections of the hipbone; together these two bones form the front of the pelvis

Other synonyms of pubis include pubic bone.

pubis (noun)	os pubis (noun)
one of the three sections of the hipbone; together these two bones form the front of the pelvis	one of the three sections of the hipbone; together these two bones form the front of the pelvis