litotes vs rhetorical device

litotes and rhetorical device both are nouns.

Word	Noun	Adjective	Verb	Adverb
litotes	Yes	No	No	No
rhetorical device	Yes	No	No	No

As nouns, rhetorical device is a hypernym of litotes; that is, rhetorical device is a word with a broader meaning than litotes:

litotes: understatement for rhetorical effect (especially when expressing an affirmative by negating its contrary)
rhetorical device: a use of language that creates a literary effect (but often without regard for literal significance)

Other hypernyms of litotes include understatement.

litotes (noun)	rhetorical device (noun)
understatement for rhetorical effect (especially when expressing an affirmative by negating its contrary)	a use of language that creates a literary effect (but often without regard for literal significance)