1. An opening constructed in a wall or roof that functions to admit light or air to an enclosure and is often framed and spanned with glass mounted to permit opening and closing. 2. A framework enclosing a pane of glass for such an opening; a sash. 3. A pane of glass or similar material enclosed in such a framework. 4. An opening that resembles a window in function or appearance. 5. The transparent panel on a window envelope. 6. The area or space immediately behind a window, especially at the front of a shop. 7. St. Petersburg was Peter the Great's window onto the Baltic. 8. a brief window of opportunity for a space mission; a window of vulnerability during which the air force was subject to attack. 9. Strips of foil dropped from an aircraft to confuse enemy radar; chaff. 10. A range of electromagnetic frequencies that pass unobstructed through a planetary atmosphere. 11. A small area on a screen in which a file or a part of a file can be displayed. 12. A launch window. 13. An area at the outer limits of the earth's atmosphere through which a spacecraft must pass in order to return safely.
