omphalus vs belly button

omphalus and belly button both are nouns.

Word	Noun	Adjective	Verb	Adverb
omphalus	Yes	No	No	No
belly button	Yes	No	No	No

As nouns, omphalus and belly button are synonyms defined as:

Other synonyms of omphalus include bellybutton, navel, omphalos, umbilicus.

omphalus (noun)	belly button (noun)
a scar where the umbilical cord was attached	a scar where the umbilical cord was attached