lion monkey vs marmoset

lion monkey and marmoset both are nouns.

Word	Noun	Adjective	Verb	Adverb
lion monkey	Yes	No	No	No
marmoset	Yes	No	No	No

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

lion monkey: small South American marmoset with silky fur and long nonprehensile tail
marmoset: small soft-furred South American and Central American monkey with claws instead of nails

lion monkey (noun)	marmoset (noun)
small South American marmoset with silky fur and long nonprehensile tail	small soft-furred South American and Central American monkey with claws instead of nails