heat engine vs engine

heat engine and engine both are nouns.

Word	Noun	Adjective	Verb	Adverb
heat engine	Yes	No	No	No
engine	Yes	No	No	No

As nouns, engine is a hypernym of heat engine; that is, engine is a word with a broader meaning than heat engine:

heat engine (noun)	engine (noun)
any engine that makes use of heat to do work	motor that converts thermal energy to mechanical work
	a wheeled vehicle consisting of a self-propelled engine that is used to draw trains along railway tracks
	an instrument or machine that is used in warfare, such as a battering ram, catapult, artillery piece, etc.
	something used to achieve a purpose