Sill 5 : A ridge or other below sea level geological formation which separates the water of one basin from another; as, for example, the ridge at the Straits of Gibralter which separates the Mediterranean from the North Atlantic
Intergovernmental Oceanographic Commission IOC technical series 37, Tsunami Glossary (A glossary of terms and acronyms used in the tsunami literature - English), , United Nations Educational, Scientific and Cultural Organization UNESCO, Paris, France 1991. http://unesdoc.unesco.org/images/0008/000885/08853 8eb.pdf, (ND/ Tsunami Sci - Brit) {590}