Jock
wiktionary
Unknown. Suggested to be a hypocoristic for John (compare Jack).
The computer slang meanings are derived from jockey. The athletic slang meanings in turn date from the middle 20th century and are simple abbreviations of jockstrap, which is in turn derived from the older slang meaning of jock itself, which dates from the 17th century, and whose etymology is unknown.
jock (third-person singular simple present jocks, present participle jocking, simple past and past participle jocked)
etymonline
jock (n.)
1952, short for jockstrap "supporter of the male genital organs," which also meant, in slang, "athletic male." Jock with the meaning "an athletic man" is from 1963, American English slang. A jockette (1948) originally was a female disk jockey, then a female jockey (1969), then an athletic female (1979).
Jock
c. 1500, variant of the masc. proper name Jack, the by-form of John. In Scotland and northern England it is the usual form. Since 1520s, like Jack, it has been used generically, as a common appellative of lads and servants, as the name of a typical man of the common folk, of a Scottish or North Country seaman, etc.
