Blackthorn (4)
I believe the answer is:
sloe
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">blackthorn</span>' is the definition.<br/ ><span class="explanation-format__explanation">(synonyms)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for sloe that I've seen before include "Blackthorn, used in making a type of gin" , "Fruit often used for gin" , "Musical study" , "Black fruit" , "Thorny bush with plum-like fruit" .)