seaboard

noun

1. The area bordering the sea; a coastline; a sealine.

   “While De Anza was exploring the Bay of San Francisco, seeking a site for the presidio, the American colonists on the eastern seaboard, three thousand miles away, were celebrating the signing of the Declaration of Independence.”

   “Recently the Great Northern Railway, U,S.A., which has a considerable mileage of line bordering the Pacific seaboard, has put in service mobile equipment for applying anti-corrosion treatment to rails.”