From Classic Encyclopedia 1911
JOCKEY, a professional rider of race-horses, now the current usage (see Horse-Racing). The word is by origin a diminutive of "Jock," the Northern or Scots colloquial equivalent of the name "John" (cf. Jack). A familiar instance of the use of the word as a name is in "Jockey of Norfolk" in Shakespeare's Richard III. v. 3, 304. In the 16th and 17th centuries the word was applied to horse-dealers, postilions, itinerant minstrels and vagabonds, and thus frequently bore the meaning of a cunning trickster, a "sharp," whence "to jockey," to outwit, or "do" a person out of something. The current usage is found in John Evelyn's Diary, 1670, when it was clearly well known. George Borrow's attempt to derive the word from the gipsy chukni, a heavy whip used by horse-dealing gipsies, has no foundation.