Fen (5)
I believe the answer is:
marsh
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">fen</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I know that fen can be written as marsh)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for marsh that I've seen before include "Waterlogged land" , "Low-lying wet land with grassy vegetation" , "eg Romney" , "Wet land; swamp" , "Fen" .)