sill

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sill / sil/ • n. a shelf or slab of stone, wood, or metal at the foot of a window or doorway. ∎  a strong horizontal member at the base of any structure, e.g., in the frame of a motor or rail vehicle. ∎  Geol. a tabular sheet of igneous rock intruded between and parallel with the existing strata. Compare with dike1 . ∎  an underwater ridge or rock ledge extending across the bed of a body of water.ORIGIN: Old English syll, sylle ‘horizontal beam forming a foundation,’ of Germanic origin; related to German Schwelle ‘threshold.’

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