The term 'sea landmass' can be broken down into two crossword solutions: ISLET (5 letters) and sea (3 letters). An ISLET is a small island, usually found in a lake or near a coastline. It is typically uninhabited and is often used as a tourist destination. The sea, on the other hand, is a large body of salt water that covers most of the Earth's surface. It is home to many different species of marine life and is an important source of food and resources for humans.