Isthmus
Isthmus (?; 277) , noun
[Latin isthmus, Greek 'isqmo`s a neck, a neck of land between two seas, an isthmus, especially the Isthmus of Corinth; prob. from the root of 'ie`nai to go; compare Icelandic eie isthmus. See Issue.]
(Geography) A neck or narrow slip of land by which two continents are connected, or by which a peninsula is united to the mainland; as, the Isthmus of Panama; the Isthmus of Suez, etc.