covered wagon vs wagon train

covered wagon and wagon train both are nouns.

Word	Noun	Adjective	Verb	Adverb
covered wagon	Yes	No	No	No
wagon train	Yes	No	No	No

covered wagon (noun)	wagon train (noun)
a large wagon with broad wheels and an arched canvas top; used by the United States pioneers to cross the prairies in the 19th century	a procession (of wagons or mules or camels) traveling together in single file