Glaring mistake (6)
I believe the answer is:
howler
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">glaring mistake</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 howler that I've seen before include "Grievous error" , "Serious avoidable mistake" , "A foolish mistake, sounds noisy" , "Bad blunder - type of monkey" , "A glaring mistake, sounds vocally noisy" .)