• (n.) The winged cap of Mercury; also, a broad-brimmed, low-crowned hat worn by Greeks and Romans.
Pet'a·sus noun [ Latin , from Greek ....] (Gr. & Rom. Antiq.) The winged cap of Mercury; also, a broad-brimmed, low-crowned hat worn by Greeks and Romans. 
A petasus or petasos was a broad-brimmed hat worn by the ancient Greeks, such as one with wings on either side as traditionally worn by Mercury.