Množina: isthmuses

ETYM Latin isthmus, Greek isthmos a neck, a neck of land between two seas, an isthmus, especially the Isthmus of Corinth; prob. from the root of ienai to go; cf. Icel. eith isthmus. Related to Issue.
Narrow strip of land joining two larger land masses. The Isthmus of Panama joins North and South America.
(Irregular plural: isthmuses).
A relatively narrow strip of land (with water on both sides) connecting two larger land areas.

Množina: Isthmus of Dariens

Isthmus of Panama.

Množina: Isthmus of Kras

Isthmus S Thailand in N central Malay Peninsula; 40 miles (64 kilometers) wide at narrowest part

Množina: Isthmus of Panamas

The isthmus that connects Central America and South America.

Množina: Isthmus of Suezs

Isthmus NE Egypt between Mediterranean and Red seas connecting Africa and Asia.

Množina: Isthmus of Tehuantepecs

The narrowest section of Mexico, between Gulf of Tehuantepec (on Pacific side) and Bay of Campeche; 137 miles (220 kilometers) wide at narrowest point.

Singular of isthmuses is isthmus.