bellybutton vs omphalus

bellybutton and omphalus both are nouns.

Word	Noun	Adjective	Verb	Adverb
bellybutton	Yes	No	No	No
omphalus	Yes	No	No	No

As nouns, bellybutton and omphalus are synonyms defined as:

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

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