wagon train vs covered wagon

wagon train and covered wagon both are nouns.

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

wagon train (noun)	covered wagon (noun)
a procession (of wagons or mules or camels) traveling together in single file	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