omphalos vs belly button

omphalos and belly button both are nouns.

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

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

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

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