Definition of water sill in English:

water sill

noun

Geology
  • 1A horizontal stratum of porous or poorly consolidated, often waterlogged, sandstone or other sedimentary rock; specifically (with the) a formation of this kind in the northern Pennines in England.

  • 2A thin layer of water trapped between strata.

Origin

Early 19th century; earliest use found in Transactions of the Geological Society.