Definition
A stain is discolored plant tissue associated with injury or plant disease.
Above: Decay stain of wood of koa (Acacia koa), associated with fungal rot of the internal trunk tissue.
Etymology. 1382, probably representing a merger of O.N. steina "to paint" and an aphetic form of M.E. disteynen "to discolor or stain," from O.Fr. desteign-, stem of desteindre "to remove the color," from des- (from L. dis- "remove") + O.Fr.
Discussion
Decay stains can greatly diminish the value of trees harvested for lumber.