Caius /ca-ius/ [3 sylls.] as a boys' name is pronounced keys. It is of Latin origin, and the meaning of Caius is happy. Common Roman form of Gaius.This was the name of the infamous Roman emperor called Caligula, a nickname meaning little boots. This referred to the minature soldier's footwear he wore when he was young. A 16th-century English physician endowed a college at Cambridge University called Gonville and Caius.aius is an uncommonly occurring first name for men. Caius is an equivalently unusual last name too for all people. (2000 U.S. Census). Below is a graphed comparison of the usage of the boy name Caius and corresponding names.