heater vs device

heater and device both are nouns.

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

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

heater (noun)	device (noun)
(baseball) a pitch thrown with maximum velocity	any clever maneuver
device that heats water or supplies warmth to a room	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