\Sill\, n. [OE. sille, sylle, AS. syl, syll; akin to G.
schwelle, OHG. swelli, Icel. syll, svill, Sw. syll, Dan.
syld, Goth. gasuljan to lay a foundation, to found.]
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:
(a) The timber or stone at the foot of a door; the threshold.
(b) The timber or stone on which a window frame stands; or,
    the lowest piece in a window frame.
(c) The floor of a gallery or passage in a mine.
(d) A piece of timber across the bottom of a canal lock for
    the gates to shut against.
{Sill course} (Arch.), a horizontal course of stone, terra
   cotta, or the like, built into a wall at the level of one
   or more window sills, these sills often forming part of
   it.

\Sill\, n. [Cf. {Thill}.]
The shaft or thill of a carriage. [Prov. Eng.]

\Sill\, n. [Cf. 4th {Sile}.]
A young herring. [Eng.]