heat engine vs ICE

heat engine and ICE both are nouns.

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

As nouns, ICE is a hyponym of heat engine; that is, ICE is a word with a more specific, narrower meaning than heat engine:

heat engine: any engine that makes use of heat to do work
ICE: a heat engine in which combustion occurs inside the engine rather than in a separate furnace; heat expands a gas that either moves a piston or turns a gas turbine

Other hyponyms of heat engine include external-combustion engine, internal-combustion engine.

heat engine (noun)	ICE (noun)
any engine that makes use of heat to do work	a heat engine in which combustion occurs inside the engine rather than in a separate furnace; heat expands a gas that either moves a piston or turns a gas turbine