Prove wrong (8)
I believe the answer is:
confound
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">prove wrong</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for confound that I've seen before include "Thwart - baffle" , "Puzzle" , "Befuddle, confuse" , "Defeat (a plan or hope)" , "Surprise; defeat (plan)" .)