Caius \caius\ as a boy's name is pronounced keys. It is of Latin origin, and the meaning of Caius is "rejoice". Variant of Gaius. A 16th-century English physician endowed a college at Cambridge University called "Gonville and Caius".

Caius has 7 variant forms: Cai, Caio, Kay, Kaye, Keye, Keyes and Keys.

Baby names that sound like Caius are Cass, Gus, Guus, Case, Casey, Cayce, Cacey, Cace, Caz and Kass.