coastline

Etymology

coast + line

noun

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.)
   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. November 2 2022, Paul Bigland, “New trains, old trains, and splendid scenery”, in RAIL, number 969, pages 56–57