| 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. |

| sill (sĭl) Pronunciation Key
A sheet of igneous rock intruded between layers of older rock. See illustration at batholith. |