Definition of "coastline"

coastline

noun
countable and uncountable, plural coastlines
1. The shape, outline, or boundary of a coast. (The term coastline is generally used to describe the approximate boundaries at relatively large spatial scales.)
  Quotations
  Tarbarrels and bonfires were lighted along the coastline of the four seas on the summits of the Hill of Howth, Three Rock Mountain, Sugarloaf, Bray Head, the mountains of Mourne, the Galtees, the Ox and Donegal and Sperrin peaks, the Nagles and the Bograghs, the Connemara hills, the reeks of M’ Gillicuddy, Slieve Aughty, Slieve Bernagh and Slieve Bloom.
  1922 February, James Joyce, “[Episode 12: Cyclops]”, in Ulysses, Paris: Shakespeare and Company, […], part II [Odyssey], page 328
  With the sea below us grey and storm swept, and the coast line vague in the driving rain, we forged our way up the bank to breast the summit at 37 m.p.h.
  1947 January and February, O. S. Nock, “"The Aberdonian" in Wartime”, in Railway Magazine, page 8
  The journey is worth an article in itself, but all I can give is a flavour of a railway which traverses a bleak but dramatic coastline that's regularly battered by the elements - especially around Parton, where the line is constantly threatened by the sea.
  2022 November 2, Paul Bigland, “New trains, old trains, and splendid scenery”, in RAIL, number 969, pages 56–57