howler monkey vs platyrrhine

howler monkey and platyrrhine both are nouns.

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

As nouns, platyrrhine is a hypernym of howler monkey; that is, platyrrhine is a word with a broader meaning than howler monkey:

howler monkey: monkey of tropical South American forests having a loud howling cry
platyrrhine: hairy-faced arboreal monkeys having widely separated nostrils and long usually prehensile tails

Other hypernyms of howler monkey include New World monkey, platyrrhinian.

howler monkey (noun)	platyrrhine (noun)
monkey of tropical South American forests having a loud howling cry	hairy-faced arboreal monkeys having widely separated nostrils and long usually prehensile tails

howler monkey (adjective)	platyrrhine (adjective)
	of or related to New World monkeys having nostrils far apart or to people with broad noses