Liber was the ancient Roman god of fertility, often called Pater Liber ('Father Liber'). He was usually worshipped with Ceres and Libera (the latter being his wife), who are the Roman equivalents of Demeter and Persephone. He came to be identified with Dionysus (otherwise Bacchus), possibly because Iacchus, the companion of Persephone, was confused by the Greeks with Bacchus.

His name seems hot to derive from Latin liber, 'free', 'unrestricted', although there may be some sort of a link since one of Dionysus' by-names is Lyaiüs, 'deliverer', 'looser' (Greek luo, 'to loose', 'release'). Perhaps it relates more to libo, 'to give a taste of, 'make an offering or libation', in view of the fact that he was the god of fertility and that rain and dew help to make the land fertile.

Reading his name this way, we can call him 'provider of moisture', even 'pourer'. His festival was called the Liberalia, and this became a favourite day for boys to don their toga virilis (their symbol of manhood) with an implicit pun on his name and Latin liberi, 'children'.