Definition of Roughrider

Babylon English Dictionary
member of the 1st U.S. Volunteer Cavalry which was established By Theodore Roosevelt to fight in the Spanish-American War (1898)
one who prepares untrained horses for riding
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Roughrider Definition from Language, Idioms & Slang Dictionaries & Glossaries
Webster's Revised Unabridged Dictionary (1913)
(n.)
One who breaks horses; especially (Mil.), a noncommissioned officer in the British cavalry, whose duty is to assist the riding master.
  
Webster's Revised Unabridged Dictionary (1913), edited by Noah Porter. About
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roughrider
\rough"rid`er\ (?), n. one who breaks horses; especially (mil.), a noncommissioned officer in the british cavalry, whose duty is to assist the riding master.
roughrider
\rough"rid`er\ (?), n. an officer or enlisted man in the 1st u. s. volunteer cavalry, a regiment raised for the spanish war of 1898, composed mostly of western cowboys and hunters and eastern college athletes and sportsmen, largely organized, and later commanded, by theodore roosevelt. sometimes, locally, a member of any of various volunteer cavalry commands raised in 1898. [colloq.]
roughrider
n : a horseman skilled at breaking wild horses to the saddle

WordNet 2.0

Noun
1. a horseman skilled at breaking wild horses to the saddle
(hypernym) horseman, equestrian, horseback rider