heating pad vs heater

heating pad and heater both are nouns.

Word	Noun	Adjective	Verb	Adverb
heating pad	Yes	No	No	No
heater	Yes	No	No	No

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

heating pad: heater consisting of electrical heating elements contained in a flexible pad
heater: device that heats water or supplies warmth to a room

Other hypernyms of heating pad include warmer.

heating pad (noun)	heater (noun)
heater consisting of electrical heating elements contained in a flexible pad	(baseball) a pitch thrown with maximum velocity
	device that heats water or supplies warmth to a room