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.
ridge; rise; horizontal layer of igneous rock between older rock beds.
Threshold or brink across the bottom of a canal lock for the gates to shut against.
From Middle English sille, selle, sulle, from Old English syll, syl, from Proto-Germanic *sulī, from Proto-Indo-European *sel-, *swel-. Cognate with Scots sil, sill, Dutch zulle ("sill"), Low German Sull, Sülle, Danish syld ("base of a framework building"), Swedish syll ("joist, cross-tie"), Norwegian syll, Icelandic syll, sylla. Related also to German Schwelle ( > Danish svelle), Old Norse svill, Latin silva ("wood, forest"), Ancient Greek ὕλη.