Short form of James, already recorded as early as the Middle Ages and now also used independently. Well-known bearers of the name have included the Scottish racing driver Jim Clark (1936–68), the British comedian Jim Davidson (b. 1953), and the Canadian actor Jim Carrey (b. 1962).
Variant spelling of French Cartret, probably a derivative of Old French cartier ‘quarter’, which, among other things, denoted a measure of land equivalent to the area which could be sown with a quart of seed.