Vinegar acid (6)
I believe the answer is:
acetic
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">vinegar acid</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 acetic that I've seen before include "really sour" , "Like the acid in vinegar" , "sort of acid" , "tart" , "Saucy'" .)