horseless

CIDE DICTIONARY

horseless, a. 

 Being without a horse; specif., not requiring a horse; -- said of certain vehicles in which horse power has been replaced by electricity, steam, etc.; as, a horseless carriage or truck. It was used primarily in the term “horseless carriage”, to refer to automobiles. By the 1930's when automobiles had become more common than horses for transportation, the term had lost its currency.  [Webster 1913 Suppl.]

OXFORD DICTIONARY

horseless, adj. without a horse.

Idiom

horseless carriage archaic a motor car.