Main Entry: sill

Pronunciation: \ˈsil\

Function: noun

Etymology: Middle English sille, from Old English syll; akin to Old High German swelli beam, threshold

Date: before 12th century

1 : a horizontal piece (as a timber) that forms the lowest member or one of the lowest members of a framework or supporting structure: as a : the horizontal member at the base of a window b : the threshold of a door
2 : a tabular body of igneous rock injected while molten between sedimentary or volcanic beds or along foliation planes of metamorphic rocks
3 : a submerged ridge at relatively shallow depth separating the basins of two bodies of water