1725, "boy who tends to cows," from cow (n.) + boy. Sense in Western U.S. is from 1849; in figurative use by 1942 for "brash and reckless young man" (as an adjective meaning "reckless," from 1920s). Cowhand is first attested 1852 in American English (see hand (n.)). Cowpoke (said to be 1881, not in popular use until 1940s) was said to be originally restricted to the cowboys who prodded cattle onto railroad cars with long poles.
