Pĕt'a-sūs, n.

noun

n. [Lat. petasus, Gr. πέτασος, a spreading or broad-brimmed hat, fr. πεταννύναι, to spread out.]

  1. (Antiq.) The winged cap of Mercury; a broad-brimmed hat.
  2. (Arch.) A cupola having the form of a broad-brimmed hat. Crabb.