Entry 1 sense Webster, 1913 Petasus · Pet·a·sus · IPA /ˈpɛtəsəs/ 01 n. The winged cap of Mercury; also, a broad-brimmed, low-crowned hat worn by Greeks and Romans. 1. The winged cap of Mercury; also, a broad-brimmed, low-crowned hat worn by Greeks and Romans.(Gr. & Rom. Antiq.)