seaboard
n.the land that is right next to the sea or ocean. It is often used to describe a long stretch of coast, like the eastern side of a country.
n.a region of land bordering the sea; the coastline or the territory adjacent to it. Often used in geopolitical or geographical contexts to refer to a specific coastal stretch of a continent.
“The storm hit the entire eastern seaboard.”
“Many major cities are located along the Atlantic seaboard to facilitate international trade and shipping.”
“The rapid industrialization of the eastern seaboard during the nineteenth century transformed small fishing villages into bustling commercial hubs that dominated the nation's economy.”
Often appears in the singular when referring to a specific coast, such as 'the Atlantic seaboard'.
“The South—and the entire Eastern seaboard , for that matter—has a similar climate to the Joros' native Japan.”
From earlier sea-bord, perhaps continuing (with change in meaning) Middle English see bord (“porthole cover, seaward side”), equivalent to sea + board.
Etymology adapted from Wiktionary, available under CC BY-SA 4.0.