Sandhill (4)
I believe the answer is:
dune
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">sandhill</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 dune that I've seen before include "Coastal sand hill" , "Sandhill" , "Low hill of sand, called in a desert a barkhan" , "Seashore sand hill" , "Ridge of sand created by wind" .)