bellybutton vs belly button

bellybutton and belly button both are nouns.

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

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

bellybutton and belly button: a scar where the umbilical cord was attached

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

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