Jock/jockey

Jock is a Scottish nickname for John since the 1500s, also informal for any Scottish soldier from more or less the same time. Jock was also slang for penis from about c.1650 but fell into disuse from the mid-19th century. Jock is also modern American slang for a male athlete or boorish overbearing male from the late 1950s. Jockey is merely the diminutive of Jock but has been used to describe riders of racehorses since the mid-1600s and has connotations of underling or someone who performs menial tasks, which was how jockeys were first perceived. See also disc jockey.