ˈskänchən noun
or scun·cheon ˈskən-
( -s )
Etymology: Middle English scouchon, skonchon, sconcheon, from Middle French escoinsson, escouchon, escochon, from coing, coin wedge, stamp, corner — more at coin
: the part of the side of an opening from the back of the reveal to the inside face of the wall usually forming in the masonry a rabbet in which the wooden frame is set