Pet form of any of the various names beginning with the letter K- (compare Dee and Jay), most notably Katherine and its many variants. It is also used independently. As a boy's name it may in part make reference to the name of the Arthurian knight Sir Kay, although he is not a particularly attractive character. His name is probably a Celticized form of Latin Gaius, an ancient Roman personal name of uncertain derivation. As a girl's name it was famous as that of the actress Kay Kendall (1926–59, original name Justine McCarthy).