Meaning

noun structural member consisting of a continuous horizontal timber forming the lowest member of a framework or supporting structure

noun (geology) a flat (usually horizontal) mass of igneous rock between two layers of older sedimentary rock

originFrom 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”),…

Etymology from Wiktionary, CC BY-SA 3.0