plaster [Gk, emplastron] , 1. any composition of a liquid and a powder that hardens when it dries, used in shaping a cast to support a fractured bone as it heals, such as plaster of paris. 2. (Informal) a home remedy consisting of a semisolid mixture applied to a part of the body as a counterirritant or for other therapeutic reasons, such as a mustard plaster.
