straightener vs device

straightener and device both are nouns.

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

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

straightener (noun)	device (noun)
a device for straightening	any clever maneuver
	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