trolley car vs horsecar

trolley car and horsecar both are nouns.

Word	Noun	Adjective	Verb	Adverb
trolley car	Yes	No	No	No
horsecar	Yes	No	No	No

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

trolley car: a wheeled vehicle that runs on rails and is propelled by electricity
horsecar: an early form of streetcar that was drawn by horses

trolley car (noun)	horsecar (noun)
a wheeled vehicle that runs on rails and is propelled by electricity	an early form of streetcar that was drawn by horses