defroster vs heater

defroster and heater both are nouns.

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

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

defroster: heater that removes ice or frost (as from a windshield or a refrigerator or the wings of an airplane)
heater: device that heats water or supplies warmth to a room

Other hypernyms of defroster include warmer.

defroster (noun)	heater (noun)
heater that removes ice or frost (as from a windshield or a refrigerator or the wings of an airplane)	(baseball) a pitch thrown with maximum velocity
	device that heats water or supplies warmth to a room