The Japanese word hannya (般若) can mean two things.
  1. Fundamental wisdom that is revealed to the one who awakens to the true life. To know the ultimate reality of the universe. prajna. Etymology: Prajñā.
  2. One of the more famous masks in noh plays. It is a mask of a female oni (i.e. a ghost or a spirit) with a facial expression of fury, jealousy, and anxiety. She has two horns and gold plated eyes and teeth. Etymology: Said to have been first created by a person named Hannyabō (般若坊).

Source: Daijirin Dictionary, edited by Akira MATSUMURA (松村明), published by Sanseido Co., Ltd. 2nd edition 1995. ISBN 4-385-13900-8. ← page in Japanese