- sill - structural member consisting of a continuous horizontal timber forming the lowest member of a framework or supporting structure
--1 is a kind of structural member
--1 has particulars: doorsill, doorstep, threshold; windowsill- sill - (geology) a flat (usually horizontal) mass of igneous rock between two layers of older sedimentary rock
--2 is a kind of rock, stone
- sill - (geology) a flat (usually horizontal) mass of igneous rock between two layers of older sedimentary rock