noun A breast wall; window breast; horizontal brink which forms the base of a window.
She looked out the window resting her elbows on the window sill.
noun A threshold; horizontal structural member of a building near ground level on a foundation or pilings, or lying on the ground, and bearing the upright portion of a frame; a sill plate.
noun A stratum of rock, especially an intrusive layer of igneous rock lying parallel to surrounding strata.
noun A threshold or brink across the bottom of a canal lock for the gates to shut against.
noun A raised area at the base of the nasal aperture in the skull.
the nasal sill
noun The inner edge of the bottom of an embrasure.