steam engine vs steam boiler

steam engine and steam boiler both are nouns.

Word	Noun	Adjective	Verb	Adverb
steam engine	Yes	No	No	No
steam boiler	Yes	No	No	No

steam engine (noun)	steam boiler (noun)
external-combustion engine in which heat is used to raise steam which either turns a turbine or forces a piston to move up and down in a cylinder	sealed vessel where water is converted to steam