A horse of a strong, agile breed developed in the western United States to work with cattle, usually having a solid-colored coat.
Any of a breed of light, muscular horse of a solid, usually dark color: because of its quick reactions it is much used in Western range work and in rodeos.
Origin of quarter-horse
- From its formerly being trained for races up to a quarter mile
From American Heritage Dictionary of the English Language, 5th Edition