Choose the correct one-word substitution for "land covered by water on three sides".

Introduction / Context:
This general knowledge and vocabulary question asks for the geographical term that describes a piece of land surrounded by water on three sides and connected to a larger landmass on the fourth side. Knowing such basic geographical terms is important for school level science and competitive exams.

Given Data / Assumptions:
The description is:

• Land covered by water on three sides.

The options are:

• Island
• Mainland
• Strait
• Peninsula

We assume standard definitions from geography textbooks.

Concept / Approach:
A peninsula is a piece of land that extends into a body of water and is surrounded by water on three sides, while still connected to the main landmass on one side. An island is surrounded by water on all sides. Mainland refers to the primary large portion of a continent or country. A strait is a narrow passage of water connecting two larger bodies of water. Therefore, peninsula is the only term that fits the given description exactly.

Step-by-Step Solution:
Step 1: Recall the definition of peninsula: a land area nearly surrounded by water but connected to a larger landmass on one side. Step 2: Compare this with the phrase land covered by water on three sides. This matches the picture of a peninsula. Step 3: Examine Island. An island is a piece of land completely surrounded by water on all sides, so it does not match three sides only. Step 4: Examine Mainland. This refers to the main continuous land part of a country or continent, not a smaller piece jutting into water. Step 5: Examine Strait. A strait is a narrow waterway connecting two larger water bodies, often lying between two land masses. It is not a piece of land at all. Step 6: Examine Peninsula. This precisely describes land almost surrounded by water, commonly on three sides, such as the Indian peninsula. Step 7: Therefore, Peninsula is the correct one-word substitution.

Verification / Alternative check:
Textbook examples include the Iberian Peninsula (Spain and Portugal) and the Indian Peninsula, each projecting into surrounding seas while attached to the larger continental landmass. If the land were completely encircled by water, like Sri Lanka or Sri Lanka island, it would be called an island instead. These examples confirm that peninsula is reserved for the three sides water, one side land situation.

Why Other Options Are Wrong:
Island is wrong because it involves water on all sides, not three. Mainland is wrong because it describes the main continuous land area, not a smaller projection into the sea. Strait is wrong because it refers to a water body, not a land form. Only peninsula matches land covered by water on three sides while being attached on one side.

Common Pitfalls:
Students sometimes confuse island and peninsula because both are surrounded by water to some extent. A simple memory aid is that an island floats alone (completely surrounded), while a peninsula sticks out but still touches the rest of the land. Another pitfall is not knowing what strait means and mistakenly choosing it. Remember that strait always refers to water, not land.

Final Answer:
The correct geographical term is Peninsula.