in the American Revolution, a band of American Tories who infested the neutral ground of Westchester County, N.Y., robbed the Whigs and Loyalists, and made a specialty of stealing cattle. The word cowboys is now used to designate the men who have charge of the cattle on the vast ranges in the W. and S.W. of the United States. Many of them were enlisted in two regiments of cavalry for the war with Spain, and, under the popular name of "Rough Riders," greatly distinguished themselves in the early part of the campaign against Santiago, in Cuba.
Entry from Everybody's Cyclopedia, 1912.