Definition of window:
(n) :
an opening, usually covered by one or more panes of clear glass, to allow light and air from outside to enter a building or vehicle; an opening, usually covered by glass, in a shop which allows people to view the shop and its products from outside
"1952: A window is an opening in a wall to admit light and air. — L.F. Salzman, Building in England, p. 173."