noun (n)

• a relatively narrow strip of land (with water on both sides) connecting two larger land areas(noun.object)

  source: wordnet30
• a cord-like tissue connecting two larger parts of an anatomical structure(noun.body)

  Synonym:
  band
  

  source: wordnet30
• 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.(noun)

  source: webster1913