an opening in the wall of a building, side of a vehicle, etc to let in light and air, usu fitted with a frame containing glass and capable of being opened and shut

a pane of glass in a window

a display area behind the window of a shop

a transparent panel in an envelope, through which the address on the enclosure is visible

in computing, a rectangular area of the display on a VDU or monitor within which a separate part of an image or file can be displayed

a brief time available for something

a window of opportunity

something that functions like a window, e.g. in allowing people to see what is normally hidden

a window on the Western world

a range of wavelengths in the electromagnetic spectrum that can pass through a planet's atmosphere

an interval of time within which a rocket or spacecraft must be launched to accomplish a particular mission

an area at the limits of the earth's atmosphere through which a spacecraft must pass for successful re-entry