sill has definitions from the field of geology
1
[ noun ] structural member consisting of a continuous horizontal timber forming the lowest member of a framework or supporting structure

Used in print

(Sallie Bingham, "Moving Day," The Atlantic...)

He noticed a speck of dirt on the sill and swiped at it with his finger .

2
[ noun ] Last name, frequency rank in the U.S. is 8882
3
[ noun ] (geology) a flat (usually horizontal) mass of igneous rock between two layers of older sedimentary rock

Related terms

rock geology

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