The term 'water route' is a type of transportation that involves the use of waterways. The two crossword solutions for this term are MAIN, which is a four-letter word, and SEAWAY, which is a six-letter word. MAIN refers to a large river or other body of water, while SEAWAY is a navigable route, usually through a canal, that connects two bodies of water. Together, these two words describe a route that is navigable by boat or ship.