Billy

Billy is an English diminutive of William, which derives from the Old French form of the Germanic name Wilhelm, composed of the elements wil (will, desire) and helm (helmet, protection). The name gained widespread use as an informal given name in its own right, particularly in American and British English-speaking cultures. Notable bearers include Billy the Kid, the American outlaw, and Billy Joel, the American musician. Related forms include Bill, Will, Willem, Wilhelm, and Guilherme.