sill

SILL, n. [L. solum; allied to solid. The primary sense is probably to lay, set or throw down.]

1. Properly, the basis of foundationof a thing; appropriately, a piece of timber on which a building rests; the lowest timber of any stucture; as the sills of a house, of a bridge, of a loom and the like.

2. The timber or stone at the foot of a door; the threshhold.

3. The timber or stone on which a window frame stands; or the lowest piece in a window frame.

4. The shaft or thill of a carriage. [Local.]