The term 'long, narrow ditch' can be described by two crossword solutions: 'TRENCH' (6 letters) and 'FOSSE' (5 letters). A TRENCH is a long, narrow ditch dug in the ground, usually for military purposes. It is typically deeper than it is wide and can be used to protect troops from enemy fire. A FOSSE is a similar type of ditch, but it is usually smaller and shallower than a TRENCH. It is often used for drainage or as a boundary marker.