Definition of sill

• n. - The basis or foundation of a thing; especially, a horizontal piece, as a timber, which forms the lower member of a frame, or supports a structure; as, the sills of a house, of a bridge, of a loom, and the like.
• n. - The timber or stone at the foot of a door; the threshold.
• n. - The timber or stone on which a window frame stands; or, the lowest piece in a window frame.
• n. - The floor of a gallery or passage in a mine.
• n. - A piece of timber across the bottom of a canal lock for the gates to shut against.
• n. - The shaft or thill of a carriage.
• n. - A young herring.