sill

Etymology 1

From Middle English sille, selle, sülle, from Old English syll, syl (“sill, threshold, foundation, base, basis”), from Proto-Germanic *sulī (“bar, sill”), from Proto-Indo-European *sel-, *swel- (“beam, board, frame, threshold”). Cognate with Scots sil, sill (“balk, beam, floor, sill”), Dutch zulle (“sill”), Low German Sull, Sülle (“threshold, ramp, sill”), German Süll, Sülle (“threshold, sill”), Danish syld (“base of a framework building”), Swedish syll (“joist, cross-tie”), Norwegian syll, Icelandic syll, sylla (“sill”). Related also to German Schwelle ( > Danish svelle), Old Norse svill, Latin silva (“wood, forest”), Ancient Greek ὕλη (húlē).

noun

1. (architecture, also "window sill") A breast wall; window breast; horizontal brink which forms the base of a window.
   She looked out the window resting her elbows on the window sill.
2. (construction) A threshold; horizontal structural member of a building near ground level on a foundation or pilings, or lying on the ground, and bearing the upright portion of a frame; a sill plate.
3. (geology) A stratum of rock, especially an intrusive layer of igneous rock lying parallel to surrounding strata.
   Minor palingenetic magmas probably were generated at this time and intruded the mantling rocks in the form of small sills and apophyses […]. 1980, Geological Survey Professional Paper, Volume 1119, U.S. Government Printing Office
   The molten rock in the sills may have ignited vast reserves of shallowly buried natural gas, much like a match applied to a gas barbecue. 2018, Tim Flannery, Europe: The First 100 Million Years, Penguin, published 2019, page 55:
4. A threshold or brink across the bottom of a canal lock for the gates to shut against.
5. (anatomy) A raised area at the base of the nasal aperture in the skull.
   the nasal sill
6. (military, historical) The inner edge of the bottom of an embrasure.

Etymology 2

Compare sile.

noun

1. (UK) A young herring.

Etymology 3

Compare thill.

noun

1. The shaft or thill of a carriage.

Etymology 4

Short for silly.

adj

1. (rare, slang) Silly.