Sentence:  The debris of his other careers was piled everywhere ; a pile of wire cages for mice from his time as a geneticist and a microscope lying on its side on the <WSD>window</WSD> sill , vertical steel columns wired for support to the open ceiling beams with spidery steel cantilevers jutting out into the air , masonry constructions on the floor from the time he was inventing his disastrous fireplace whose smoke would pass through a whole house , visible all the way up through wire gratings on each floor . 
Meaning of the word marked with <WSD> tags:  the sill of a window; the horizontal member at the bottom of the window frame