Simplified diagram

An isthmus is a narrow strip of land, bordered on two sides by water, and connects two larger land masses. The term is pronounced “IS-mus” with a silent th. The plural form can either be isthmuses or isthmi.

The most famous isthmus is Panama, which connects the North and South American continents. Other isthmuses include:

Because isthmuses are narrow, they are logical places to build canals. The Panama Canal, which connects the Atlantic and Pacific Oceans, drastically cut down on the naval travel time between the east and west coasts of the Americas. The previously mentioned Suez Canal is also another good example—its construction made travel between Europe and Asia much, much shorter.

Isthmuses are the duals of straits. That is, while isthmuses lie between two bodies of water and joins two larger land masses, straits lie between two land masses and connects two larger bodies of water.

See also: geography, Mainland