sill

1. (also window sill) A horizontal slat which forms the base of a window.
2. A horizontal, structural member of a building near ground level on a foundation or pilings or lying on the ground in earth-fast construction and bearing the upright portion of a frame. Also called a ground plate, groundsill, sole, sole-plate, mudsill. An interrupted sill fits between posts instead of being below and supporting the posts in timber framing.
3. A horizontal layer of igneous rock between older rock beds.
4. A piece of timber across the bottom of a canal lock for the gates to shut against.
5. A raised area at the base of the nasal aperture in the skull.

   the nasal sill

6. The inner edge of the bottom of an embrasure.

noun

A young herring.

noun

The shaft or thill of a carriage.