Direct Opposites:
* Island: An island is a landmass completely surrounded by water, while a peninsula is only partially surrounded.
* Continent: A continent is a very large landmass, while a peninsula is a smaller extension of a larger landmass.
Related Concepts:
* Inland: This refers to areas that are not near the coast, which is the opposite of a peninsula's coastal location.
* Interior: Similar to "inland," this refers to the central part of a landmass, as opposed to a peninsula's position on the edge.
Descriptive Antonyms:
* Enclosed: This emphasizes the lack of a connection to a larger landmass, contrasting with a peninsula's connection.
* Isolated: This emphasizes the separation from other landmasses, which is not characteristic of a peninsula.
Ultimately, the best antonym depends on the specific context and the emphasis you want to convey.