belly laugh vs thigh-slapper

belly laugh and thigh-slapper both are nouns.

Word	Noun	Adjective	Verb	Adverb
belly laugh	Yes	No	No	No
thigh-slapper	Yes	No	No	No

As nouns, belly laugh and thigh-slapper are synonyms defined as:

Other synonyms of belly laugh include howler, riot, scream, sidesplitter, wow.

belly laugh (noun)	thigh-slapper (noun)
a joke that seems extremely funny	a joke that seems extremely funny
a burst of deep loud hearty laughter