A 16th century word that meant penis, that evolved to the word Jock in the 19th Century which meant to engage in sexual intercourse.
Today, the evolved word JOCK refers to a person who is athletic but with a negative connotation or association.
In its original usage, the term was used to refer to the male penis, and in its early evolution to Jock, was considered a vulgar term, that implied a person had carnal knowledge of a woman.
The implication being, the two were not married.
To Jock or Jockum Cloy as defined in Captain Francis Grose dictionary of vulgar terms (1811) as to having sex with a woman, to 'know a woman'.