window

• win‧dow [countable]
• 1 a space or an area of glass in the wall of a building or vehicle that lets in light
• open/close/shut a window
• Do you mind if I open the window?
• out of/from/through the window
• She looked out of the window to see if it was raining.
• The sun was shining through the windows.
• in the window (=just inside a window)
• We were looking at the Christmas displays in the shop windows.
• bedroom/kitchen etc window
• ➔ bay window, dormer window, french windows, picture window,sash window
• 2 one of the separate areas on a computer screen where different programs are operating
• 3 also window of opportunity a short period of time that is available for a particular activity:
• Delay might open a window of opportunity for their rivals.
• 4 an area on an envelope with clear plastic in it which lets you see the address written on the letter inside the envelope
• 5

  a window on/to the world

   something that makes it possible to see and learn about what is happening in other parts of the world:
• Television provides us with a useful window on the world.
• 6

  go out (of) the window

  informal to disappear completely or no longer have any effect:
• One glass of wine, and all my good intentions went out the window.

Definition from the Longman Dictionary of Contemporary English
Advanced Learner's Dictionary.