bank

noun

An elevation of the sea floor located on a continental (or island) shelf and over which the depth of water is relatively shallow (20-200m) but sufficient for surface navigation; a shallow area consisting of shifting forms of silt, sand, mud, gravel, etc., but in this case it is only used with a qualifying word such as sandbank, gravelbank, etc. A bank may support shoals or bars on its surface which render it dangerous to navigation.