Sill

(1) The 2 X 4 or 2 X 6 wood plate framing member that lays flat against and bolted to the foundation wall (with anchor bolts) and upon which the floor joists are installed. Normally the sill plate is treated lumber. (2) The member forming the lower side of an opening, as a door sill or window sill. Horizontal member at the bottom of a door or window frames to provide support and closure.