mare clausum
noun
ma·re clau·sum ˈmär-(ˌ)ā-ˈklau̇-səm 
-ˈklȯ-
-ˈklȯ- : a navigable body of water (such as a sea) that is under the jurisdiction of one nation and is closed to other nations
Word History
Etymology
New Latin, literally, closed sea
First Known Use
1652, in the meaning defined above