The term 'ARM OF A SEA' can be solved by two crossword solutions: INLET (5 letters) and ESTUARY (7 letters). An INLET is a narrow body of water that connects to a larger body of water, such as a sea or ocean. Estuaries are partially enclosed bodies of water where freshwater from rivers and streams mixes with saltwater from the ocean. Estuaries are often found at the mouths of rivers and are important habitats for many species of fish, birds, and other wildlife.