sill

(architecture, also "window sill") A breast wall; window breast; horizontal brink which forms the base of a window.

(construction) 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.

(geology) A stratum of rock, especially an intrusive layer of igneous rock lying parallel to surrounding strata.

A threshold or brink across the bottom of a canal lock for the gates to shut against.

(anatomy) A raised area at the base of the nasal aperture in the skull.

(military, historical) The inner edge of the bottom of an embrasure.