Sill

Noun

 * 1) (also window sill) A horizontal slat which forms the base of a window.
 * She looked out the window resting her elbows on the window sill.
 * 1) A horizontal member bearing the upright portion of a frame.
 * 2) A horizontal layer of igneous rock between older rock beds.

Thesaurus
base, basement, basis, bearing wall, bed, bedding, bedrock, doorsill, doorstone, floor, flooring, fond, footing, foundation, fundament, fundamental, ground, grounds, groundsel, groundwork, hardpan, mudsill, pavement, principle, radical, riprap, rock bottom, rudiment, seat, solid ground, solid rock, stereobate, stylobate, substratum, substruction, substructure, terra firma, threshold, underbuilding, undercarriage, undergirding, underpinning, understruction, understructure, window sill