(also chiefly Building cill )
■ noun
1》 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.
2》 Geology a tabular sheet of igneous rock intruded between and parallel with the existing strata. Compare with dyke 1 .
3》 an underwater ridge or rock ledge extending across the bed of a body of water.
Origin
OE syll , sylle 'horizontal beam forming a foundation', of Gmc origin.