The term RIVER PART can be broken down into two crossword solutions: DELTA (5 letters) and MOUTH (5 letters). A DELTA is a triangular landform created by sediment deposits at the MOUTH of a river. It is formed when the river splits into multiple distributaries, depositing the sediment it carries in the form of a triangle. The MOUTH of a river is the point where the river empties into another body of water, such as an ocean, lake, or another river.