What a peninsula is: A peninsula is a piece of land almost entirely surrounded by water, with a narrow connection to a larger landmass.
Possible antonyms:
* Island: A body of land completely surrounded by water. This is the most direct opposite in terms of being surrounded by water.
* Continent: A large landmass, the opposite in terms of size and being connected to other landmasses.
* Mainland: The main body of land of a country or continent, emphasizing the connection to a larger landmass.
* Interior: This focuses on the opposite of being surrounded by water, highlighting a land area far from the coast.
The best choice depends on the context:
* If you're talking about the geographical definition, "island" is the closest.
* If you're talking about the connection to a larger landmass, "island" or "mainland" might be more appropriate.
* If the size is the main difference, "continent" might be the best fit.
Let me know if you can provide more context about how you're using the word "peninsula" and I can give you a more precise antonym.