Derived from milk (6)
I believe the answer is:
lactic
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">derived from milk</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 lactic that I've seen before include "The acid found in milk" , "Kind of acid" , "The acid in sour milk" , "Relating to milk" , "Obtained from milk" .)