Defeat thoroughly (6)
I believe the answer is:
thrash
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">defeat thoroughly</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for thrash that I've seen before include "worst > party" , "Clobber" , "Beat hard" , "Beat with stick or whip" , "Punish" .)