sills is a form of:

Sill



noun
1.
(a strip of stone or wood or metal at the base of a window or door base or foundation) គែមរឺគ្រោង (ទ្វារ បង្អួច) ធ្វើពី ឈើរឺថ្ម ។ល។
ENGLISH MEANING
noun
1.
The timber or stone on which a window frame stands; or, the lowest piece in a window frame.
2.
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.
3.
The timber or stone at the foot of a door; the threshold.
4.
The floor of a gallery or passage in a mine.
5.
A piece of timber across the bottom of a canal lock for the gates to shut against.
6.
The shaft or thill of a carriage.
7.
A young herring.