navel vs belly button

navel and belly button both are nouns.

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

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

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

navel (noun)	belly button (noun)
a scar where the umbilical cord was attached	a scar where the umbilical cord was attached
the center point or middle of something