marmoset vs New World monkey

marmoset and New World monkey both are nouns.

Word	Noun	Adjective	Verb	Adverb
marmoset	Yes	No	No	No
New World monkey	Yes	No	No	No

As nouns, New World monkey is a hypernym of marmoset; that is, New World monkey is a word with a broader meaning than marmoset:

marmoset: small soft-furred South American and Central American monkey with claws instead of nails
New World monkey: hairy-faced arboreal monkeys having widely separated nostrils and long usually prehensile tails

Other hypernyms of marmoset include platyrrhine, platyrrhinian.

marmoset (noun)	New World monkey (noun)
small soft-furred South American and Central American monkey with claws instead of nails	hairy-faced arboreal monkeys having widely separated nostrils and long usually prehensile tails