Completely defeat (9)
I believe the answer is:
overwhelm
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">completely defeat</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 overwhelm that I've seen before include "Bury or drown beneath a huge mass of something" , "Swamp - have a strong emotional effect on" , "Too much" , "Crush" , "Overcome by superior force" .)