Kay \kay\ as a boy's name (also used as girl's name Kay), is of Latin and Old Welsh origin, and the meaning of Kay is "happy, rejoicing". From Gaius. Ancient name borne, in legend, by a knight of the Round Table. Now more common as a woman's name.
Kay has 2 variant forms: Kai and Keh.
For more information, see also related names Keyes and Caius.