window seat

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A seat next to a window, as in the recess of a bay window or on a bus or airplane.

from The Century Dictionary.

• noun A seat in the recess of a window.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun A typically soft seat placed in a recess, for a window, in a wall, and filling the recess.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a bench or similar seat built into a window recess