Blackcurrant cordial (6)
I believe the answer is:
cassis
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">blackcurrant cordial</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 cassis that I've seen before include "Syrupy blackcurrant liqueur" , "Blackcurrant cordial" , "French blackcurrant mixer" , "Blackcurrant syrup" , "Blackcurrent liqueur" .)