howler vs thigh-slapper

howler and thigh-slapper both are nouns.

Word	Noun	Adjective	Verb	Adverb
howler	Yes	No	No	No
thigh-slapper	Yes	No	No	No

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

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

howler (noun)	thigh-slapper (noun)
a glaring blunder	a joke that seems extremely funny
monkey of tropical South American forests having a loud howling cry
a joke that seems extremely funny