1. A continuous horizontal timber forming the lowest member of a framework or supporting structure.
2. (Geology) A flat (usually horizontal) mass of igneous rock between two layers of older sedimentary rock.
Sheet of igneous rock created by the intrusion of magma (molten rock) between layers of pre-existing rock. (A dyke, by contrast, is formed when magma cuts across layers of rock.) An example of a sill in the UK is the Great Whin Sill, which forms the ridge along which Hadrian’s Wall was built.
A sill is usually formed of diabase, a rock that is extremely resistant to erosion and weathering, and often forms ridges in the landscape or cuts across rivers to create waterfalls.
Bord en saillie. Le rebord d'une fenętre, d'une assiette ŕ soupe.
1. Pas de la porte.
3. (Au figuré) Début. Au seuil de la vie.