Narrow ditch (6)
I believe the answer is:
trench
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">narrow ditch</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for trench that I've seen before include "A military ditch for soldiers" , "at the front" , "Gutter" , "A deep ditch, as dug for troops" , "Drain" .)