different between coastline vs seabank

English

coast +? line

coastline (countable and uncountable, plural coastlines)

From Middle English see-banke, se-banke, see banke, equivalent to sea +? bank.

seabank (plural seabanks)

A bank or mole to defend against the sea.
- c. 1860, Charles Kingsley, The Fens
  So strong is the barrier which these sea-borne sands oppose to the river-borne ooze, that as soon as a seabank is built — as the projectors of the Victoria County have built them — across any part of the estuary, the mud caught by it soon 'warps' the space within into firm and rich dry land.
- 2009, Peter Murphy, The English Coast: A History and a Prospect (page 55)
  Typically, aerial photography of areas of seabanks shows a complex pattern of banks and counter-walls […]
The seashore.

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