From Longman Dictionary of Contemporary Englishisthmusisth‧mus /ˈɪsməs/ noun [countable] SGa narrow piece of land with water on both sides, that connects two larger areas of land the Isthmus of Panama
Examples from the Corpus
isthmus• He walked on, crossed the isthmus, and passed the entrance to the docks.• Picked a catena from the summit to the isthmus on the east side.Origin isthmus (1500-1600) Latin Greek isthmos 