Armorica

... means 'on (or by) the sea'.

According to Wikipedia, Armorica was "the part of Gaul between the Seine and the Loire that includes the Brittany Peninsula, extending inland to an indeterminate point and down the Atlantic Coast." According to Britannica, however, it was "[the] Latin name for the northwestern extremity of Gaul, now Brittany. In Celtic, Roman, and Frankish times Armorica also included the western part of what later became Normandy."

The Free Dictionary gives three definitions, all of which pretty much equate Armorica and Brittany: "An ancient and literary name for the northwest part of France, especially Brittany", "an ancient name for Brittany", and "an ancient region in NW France, corresponding generally to Brittany."