1. [late 18C–mid-19C] a man.
2. [mid–late 19C] (UK Und.) the expert, the exemplar.
3. any form of worker.
(a) [mid-19C–1940s] an accomplice or assistant, usu. of a driver of a cab or utility vehicle.
(b) [mid-19C+] a worker in a particular job, e.g. swab jockey, washer-up, pump jockey, petrol pump attendant, grunt-and-squeal jockey, a stock hauler, juice jockey, a gasoline-truck driver, suicide jockey, a nitro-glycerine hauler, disc jockey.
(c) [1910s+] any form of driver, esp. of cabs, buses.
4. [late 19C] (Aus.) a tramp who illegally rides freight trains.
5. [1900s–30s] (US Und.) a horse thief.
6. [1930s] a pimp.
7. [1930s] (UK Und.) a gang member.
8. [1930s+] a whore’s client.
9. [1940s+] (US) in homosexual uses.
(a) a homosexual tramp.
(b) a masculine lesbian.
10. [1950s] (gypsy) a general term of address, e.g. Hello jockey.
11. (UK Und.) a policeman.
12. [1950s–70s] a user of drugs or one who is habituated, e.g. hop-jockey, drug addict, horse-jockey, heroin user.
13. [1990s+] (Irish und.) a sex offender, a rapist.
[1990s+] (Irish) sexual intercourse and a slice of bacon.