The source name was popular in ancient Rome. It was the given personal name of the infamous Roman emperor usually called Caligula, a nickname meaning ''little boots.'' This refered to the minature soldier's footgear he wore as a small boy growing up in his father's legionary camps.
The name Kay ranked 272nd in popularity for females of all ages in a sample of the 1990 US Census.
This name is highly rated in the 1990 U.S. Census popularity survey of all ages, but after 1960 does not appear in the state data listing the most popular baby names.
Though the male Kay probably comes from the Latin name Gaius, meaning ''happy,'' this female version more likely started as a nickname for names beginning with the letter K, especially Katherine, Karen and Kathryn.