freight car vs tank

freight car and tank both are nouns.

Word	Noun	Adjective	Verb	Adverb
freight car	Yes	No	No	No
tank	Yes	No	Yes	No

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

Other hyponyms of freight car include boxcar, cattle car, coal car, flat, flatbed, flatcar, gondola, gondola car, refrigerator car, tank car.

freight car (noun)	tank (noun)
a railway car that carries freight	a large (usually metallic) vessel for holding gases or liquids
	an enclosed armored military vehicle; has a cannon and moves on caterpillar treads
	a freight car that transports liquids or gases in bulk
	a cell for violent prisoners
	as much as a tank will hold

freight car (verb)	tank (verb)
	treat in a tank
	consume excessive amounts of alcohol
	store in a tank by causing (something) to flow into it