Decomposing (6)
I believe the answer is:
rotten
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">decomposing</span>' is the definition.<br/ ><span class="explanation-format__explanation">(thesaurus)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for rotten that I've seen before include "Falling to pieces from age or morally contemptible" , "Decayed or despicable" , "Decaying - quite putrid" , "Decomposed" , "Suffering from decay" .)