belly button vs bellybutton

belly button and bellybutton both are nouns.

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

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

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

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

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