Pronunciation: (sil),[key] —n. 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. See diag. under double-hung. 3. Geol.a tabular body of intrusive igneous rock, ordinarily between beds of sedimentary rocks or layers of volcanic ejecta.