Jack

Jack is an English given name that developed in the medieval period as a pet form of John, itself derived from the Hebrew Yohanan, meaning God is gracious. The transition from John to Jack likely passed through the intermediate form Jankin, which was shortened and altered over time. The name was so common in medieval England that it became a generic word for any man, reflected in expressions such as lumberjack and flapjack. Related forms include John, Jan, and the diminutive Jackie, while Jackson originated as a surname meaning son of Jack.