The only thing islands, isthmuses, and peninsulas have in common is that they are all landmasses.

Here's a breakdown of their differences:

* Island: A piece of land completely surrounded by water.

* Isthmus: A narrow strip of land connecting two larger landmasses, often with water on either side.

* Peninsula: A piece of land surrounded by water on three sides, with a narrow connection to a larger landmass.

So, while they are all landmasses, they have different geographical characteristics and relationships with water.