noun

• (fl. AD 130–180) a celebrated Roman jurist.
• Gaius, sometimes spelled Gajus, Kaius, Cajus, Caius, was a common Latin praenomen; see Gaius (praenomen).
• a Latin praenomen, or personal name, and was one of the most common names throughout Roman history.
• the Greek spelling for the male Roman name Caius, a figure in the New Testament of the Bible.
• a genus of large mygalomorph spiders in the family Idiopidae.