From wiki:The Latin word for a dragon, draco (genitive: draconis), actually means snake or serpent, emphasising the European association of dragons with snakes. The Medieval Biblical interpretation of the Devil being associated with the serpent who tempted Adam and Eve, thus gave a snake-like dragon connotations of evil. Generally speaking, Biblical literature itself did not portray this association (save for the book of Revelations, whose treatment of dragons is detailed below). The demonic opponents of God, Christ, or good Christians have commonly been portrayed as reptilian or chimeric.