device vs mnemonic

device and mnemonic both are nouns.

Word	Noun	Adjective	Verb	Adverb
device	Yes	No	No	No
mnemonic	Yes	Yes	No	No

As nouns, mnemonic is a hyponym of device; that is, mnemonic is a word with a more specific, narrower meaning than device:

Other hyponyms of device include fast one, trick.

device (noun)	mnemonic (noun)
any clever maneuver	a device (such as a rhyme or acronym) used to aid recall
an instrumentality invented for a particular purpose
an emblematic design (especially in heraldry)
any ornamental pattern or design (as in embroidery)
something in an artistic work designed to achieve a particular effect

device (adjective)	mnemonic (adjective)
	of or relating to or involved the practice of aiding the memory