SILL n. 2 definitions
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. Hence:
STIRRUP n.
A kind of ring, or bent piece of metal, wood, leather, or the like, horizontal in one part for receiving the foot of a rider, and attached by a strap to the saddle, -- used to assist a person in mounting a horse, and to enable him to sit steadily in riding, as well as to relieve him by supporting a part of the weight o…