Window  n. 1 a opening in a wall etc., usu. With glass to admit light etc. B the glass itself. 2 space for display behind the window of a shop. 3 window-like opening. 4 opportunity to learn from observation. 5 transparent part in an envelope showing an address. 6 vdu display showing a particular part of the data.  windowless adj. [old norse, = wind-eye]