bellybutton vs umbilicus

bellybutton and umbilicus both are nouns.

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

As nouns, bellybutton and umbilicus are synonyms defined as:

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

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