Roman name which was derived from Latin hilaris meaning "cheerful". Alternatively, it could be derived from the Greek name ‘Ιλαρος (Hilaros) also meaning "cheerful" (the Greek word ‘ιλαρος 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.