railroad train vs engine

railroad train and engine both are nouns.

Word	Noun	Adjective	Verb	Adverb
railroad train	Yes	No	No	No
engine	Yes	No	No	No

railroad train (noun)	engine (noun)
public transport provided by a line of railway cars coupled together and drawn by a locomotive	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