win·dow / ˈwindō/ • n. 1. an opening in the wall or roof of a building or vehicle that is fitted with glass or other transparent material in a frame to admit light or air and allow people to see out. ∎  a pane of glass filling such an opening: thieves smashed a window and took $600. ∎  an opening in a wall or screen through which customers are served in a bank, ticket office, or similar building. ∎  a space on the inside of a store's window where goods are displayed for sale: I prefer the red dress that's in the window [as adj.] beautiful window displays. 2. a thing resembling such an opening in form or function, in particular: ∎  a transparent panel on an envelope to show an address. ∎  Comput. a framed area on a display screen for viewing information. ∎  (window on/into/to) a means of observing and learning about: television is a window on the world. ∎  Physics a range of electromagnetic wavelengths for which a medium (esp. the atmosphere) is transparent.3. an interval or opportunity for action: February 15 to March 15 should be the final window for new offers. ∎  an interval during which atmospheric and astronomical circumstances are suitable for the launch of a spacecraft.4. strips of metal foil or metal filings dispersed in the air to obstruct radar detection.PHRASES: go out the window inf. (of a plan or pattern or behavior) no longer exist; disappear.window of opportunity a favorable opportunity for doing something that must be seized immediately if it is not to be missed.window of vulnerability an opportunity to attack something that is at risk (esp. as a cold war claim that America's land-based missiles were easy targets for a Soviet first strike).windows of the soul organs of sense, esp. the eyes.DERIVATIVES: win·dow·less adj. (in sense 1).ORIGIN: Middle English: from Old Norse vindauga, from vindr ‘wind’ + auga ‘eye.’