colobus vs Old World monkey

colobus and Old World monkey both are nouns.

Word	Noun	Adjective	Verb	Adverb
colobus	Yes	No	No	No
Old World monkey	Yes	No	No	No

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

colobus: arboreal monkey of western and central Africa with long silky fur and reduced thumbs
Old World monkey: of Africa or Arabia or Asia; having nonprehensile tails and nostrils close together

Other hypernyms of colobus include catarrhine.

colobus (noun)	Old World monkey (noun)
arboreal monkey of western and central Africa with long silky fur and reduced thumbs	of Africa or Arabia or Asia; having nonprehensile tails and nostrils close together