belly button vs omphalos

belly button and omphalos both are nouns.

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

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

Other synonyms of belly button include bellybutton, navel, omphalus, umbilicus.

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