Jockey
late 16th century: diminutive of Jock. Originally the name for an ordinary man, lad, or underling, the word came to mean ‘mounted courier’, hence the current sense (late 17th century). Another early use ‘horse-dealer’ (long a byword for dishonesty) probably gave rise to the verb sense ‘manipulate’, whereas the main verb sense probably relates to the behaviour of jockeys manoeuvring for an advantageous position during a race.
wiktionary
The word is by origin a diminutive of jock, the Northern English or Scots colloquial equivalent of the first name John, which is also used generically for "boy" or "fellow" (compare Jack, Dick), at least since 1529. 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. Equivalent to jock + -ey.
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 the verb to jockey, "to outwit" or "to do" a person out of something. The current meaning of a person who rides a horse in races was first seen in 1670.
Another possible origin is the Gaelic word eachaidhe, a "horseman" (pronounced YACH-ee-yuh in late medieval times, with the ch pronounced as in German). The Irish name Eochaid (YO-ked) is related to each (yek) "horse" and is usually translated as "horse rider". This is phonetically very similar to jockey. More: https://en.wikipedia.org/wiki/Jockey#Etymology
etymonline
jockey (n.)
"person who rides horses in races," 1660s, a specific use of the earlier sense "boy, fellow" (1520s), which is a special use of the Scottish proper name Jockey, a familiar or diminutive form of Jock. Jockey-boots are from 1680s; jockey-shorts "abbreviated underwear for men" is from 1935 (jockey-briefs from 1946).
jockey (v.)
1708, "trick, outwit, gain advantage," from jockey (n.) perhaps in its former secondary sense of "horse trader" (1680s) and reflecting their reputation. Meaning "to ride a horse in a race" is from 1767. Related: Jockeyed; jockeying.
