the sill under a window.
Also, window sill.

1695–1705; window + sill Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2014.
Cite This Source Link To window sill
World English Dictionary
windowsill (ˈwɪndəʊˌsɪl)
a sill below a window

Collins English Dictionary - Complete & Unabridged 10th Edition
2009 © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins
Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009
Cite This Source
Example sentences
From time to time a living torch would be seen crouched on a window sill and
  then leaping through the air.
As a rule, you think of the ego as one who is peering out of your own eyes as
  if leaning on a window sill, looking at the world.
Placing the plant on a window sill or in a hanging basket is not safe enough.
Openings generally have stone lintels, and stone string courses wrap the
  building at the window sill level.
Copyright © 2014, LLC. All rights reserved.
  • Please Login or Sign Up to use the Recent Searches feature