steam boiler vs steam engine

steam boiler and steam engine both are nouns.

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

steam boiler (noun)	steam engine (noun)
sealed vessel where water is converted to steam	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