isthmus

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. A narrow strip of land connecting two larger masses of land.
2. n. Anatomy A narrow strip of tissue joining two larger organs or parts of an organ.
3. n. Anatomy A narrow passage connecting two larger cavities.

Century Dictionary and Cyclopedia

1. n. A narrow strip of land bordered by water and connecting two larger bodies of land, as two continents, a continent and a peninsula, or two parts of an island. The two isthmuses of most importance are that of Suez, connecting Asia and Africa, and that of Panama or Darien, connecting North and South America. The isthmus most famous in ancient times is that of Corinth, called distinctively the Isthmus, separating the Peloponnesian peninsula from the mainland of Greece. A small isthmus is often called a neck.
2. n. In botany and zoology, some connecting part or organ, especially when narrow or joining parts larger than itself.
3. n. The contracted passage from the cavity of the mouth into that of the pharynx. It is bounded above by the pendulous veil of the palate and uvula, at the sides by the pillars of the fauces, and below by the base of the tongue. More fully called isthmus faucium, isthmus of the fauces.
4. n. In fishes, the lower part of the septum between the opposing gill-openings. It is supported and stiffened by the urohyal.

Wiktionary

1. n. A narrow strip of land, bordered on both sides by water, and connecting two larger landmasses.
2. n. anatomy Any such narrow part connecting two larger structures.

GNU Webster's 1913

1. n. (Geog.) A neck or narrow slip of land by which two continents are connected, or by which a peninsula is united to the mainland

WordNet 3.0

1. n. a cord-like tissue connecting two larger parts of an anatomical structure
2. n. a relatively narrow strip of land (with water on both sides) connecting two larger land areas