Acid fruit (4)
I believe the answer is:
lime
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">acid fruit</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for lime that I've seen before include "Type of stone" , "Round green fruit or a linden tree" , "Kind of tree or substance used in cement" , "Green fruit -- green colour" , "Bright light green" .)