streetcar vs horsecar

streetcar and horsecar both are nouns.

Word	Noun	Adjective	Verb	Adverb
streetcar	Yes	No	No	No
horsecar	Yes	No	No	No

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

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

streetcar (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