If a unicycle has one wheel, and a bicycle has two, and a tricycle has three, why do...

[astrospy]

...they call a car a car? I mean where does the word "car" come from?

[Greyhawk]

Henry Ford's first experimental vehicle, in 1896, was called a quadricycle. The alternative name car is believed to originate from the Latin word carrus or carrum ("wheeled vehicle"), or the Middle English word carre ("cart") (from Old North French), or karros (a Gallic wagon).

[Greyhawk]

Henry Ford's first experimental vehicle, in 1896, was called a quadricycle. The alternative name car is believed to originate from the Latin word carrus or carrum ("wheeled vehicle"), or the Middle English word carre ("cart") (from Old North French), or karros (a Gallic wagon).

[Littlemswright]

I'm not going to swear this is the correct answer but I think "car" is an abbreviation of carriage.

[old lady]

They used to be called motorized carriages, when they were first invented. The difference between the vehicles you listed and the automobile, is that cars are not self-propelled, and the others are.