what are large masses of land surrounded by water on 3 sides called ?

peninsula = almost an island -- from the two Latin words that mean "almost" (paene) and "island" (insula)

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Large masses of land surrounded by water on three sides are called peninsulas. The word "peninsula" comes from two Latin words, "paene" meaning "almost" and "insula" meaning "island." A peninsula is similar to an island, but it is connected to the mainland by a narrow strip of land called an isthmus. For example, the Iberian Peninsula, which is made up of Spain and Portugal, is surrounded by water on three sides - the Atlantic Ocean to the west and south, and the Mediterranean Sea to the east. Peninsula is the correct term to describe such landforms.