(1):

(n.) One who breaks horses; especially (Mil.), a noncommissioned officer in the British cavalry, whose duty is to assist the riding master.

(2):

(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.