Definition of "Jock"

- - - If you want a Scotch name why don't you call him Jock?" Macgregor looked disgusted. "Because Jock is not a name, but a diminutive, as everybody knows well. It is the diminutive of John. And John is not a Scots name. The Scots form of that name is Ian. If you want to call him Ian Fetch, I shall say no more.

1975, Robertson Davies, World of Wonders, page 736