railroad car vs coach

railroad car and coach both are nouns.

Word	Noun	Adjective	Verb	Adverb
railroad car	Yes	No	No	No
coach	Yes	No	Yes	No

As nouns, coach is a hyponym of railroad car; that is, coach is a word with a more specific, narrower meaning than railroad car:

railroad car (noun)	coach (noun)
a wheeled vehicle adapted to the rails of railroad	a carriage pulled by four horses with one driver
	a railcar where passengers ride
	a vehicle carrying many passengers; used for public transport
	a person who gives private instruction (as in singing, acting, etc.)
	(sports) someone in charge of training an athlete or a team

railroad car (verb)	coach (verb)
	teach and supervise (someone); act as a trainer or coach (to), as in sports
	drive or operate a coach or carriage