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Dictionary Definition of sill
sill noun 1. a horizontal timber, block, or the like, serving as a foundation of a wall, house, etc. 2. the horizontal piece or member beneath a window, door, or other opening. 3. Geology a tabular body of intrusive igneous rock, ordinarily between beds of sedimentary rocks or layers of volcanic ejecta. [ME sille, OE syl, syll ( e ), c. LG süll; akin to G Schwelle ] |