1. A neck of land by which two continents are connected, or by which a peninsula is united to the mainland.

Nuttall's Standard dictionary of the English language By Nuttall, P.Austin

• asthmas,
• isthis,
• ithsmus,
• istmus,
• agisthus,
• arthamus,
• usthmus,
• jsthmus,
• ksthmus,
• osthmus,
• 9sthmus,
• 8sthmus,
• isthmuss,
• isthmes,
• astomus,
• bismthous,
• Astimus,
• isthmas,
• IsTHM,
• ISHMu

• isthmian,
• isthmi,
• Isthmuses.

The adjective form of the word "isthmus" is "isthmic".

The plural form of the word "isthmus" is "isthmuses" or "isthmi", though "isthmuses" is more commonly used.

The singular form of the word "isthmus" remains the same: isthmus.