Hilarius

Roman name derived from Latin hilaris meaning "cheerful". Alternatively, it could be derived from the Greek name Ἱλαρός (Hilaros) also meaning "cheerful" (the Greek word ἱλαρός was the source of the Latin word hilaris). Saint Hilarius was a 4th-century theologian and bishop of Poitiers. This was also the name of a 5th-century pope.