opera cloak vs cloak

opera cloak and cloak both are nouns.

Word	Noun	Adjective	Verb	Adverb
opera cloak	Yes	No	No	No
cloak	Yes	No	Yes	No

As nouns, cloak is a hypernym of opera cloak; that is, cloak is a word with a broader meaning than opera cloak:

opera cloak (noun)	cloak (noun)
a large cloak worn over evening clothes	a loose outer garment
	anything that covers or conceals

opera cloak (verb)	cloak (verb)
	cover with or as if with a cloak
	cover as if with clothing
	hide under a false appearance