Be mistaken (3)
I believe the answer is:
err
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">be mistaken</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 err that I've seen before include "Stray from the straight and narrow" , "Miscalculate" , "Blunder" , "Boob" , "Make a wrong move" .)