howler vs howler monkey

howler and howler monkey both are nouns.

Word	Noun	Adjective	Verb	Adverb
howler	Yes	No	No	No
howler monkey	Yes	No	No	No

As nouns, howler and howler monkey are synonyms defined as:

howler and howler monkey: monkey of tropical South American forests having a loud howling cry

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