Farmland unit (4)
I believe the answer is:
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">farmland unit</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for acre that I've seen before include "Unit of land area" , "Not a lot of land" , "marine location in Israel" , "region of ground" , "Imperial unit of area" .)