Turn rancid (3)
I believe the answer is:
rot
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">turn rancid</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 rot that I've seen before include "Decay, moulder" , "crumble" , "'Decay, decompose (3)'" , "Corruption" , "Deterioration" .)