Minor inadvertent mistake (4-2)
I believe the answer is:
slip-up
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">minor inadvertent mistake</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 slip-up that I've seen before include "Minor lapse" , "Minor inadvertent mistake" , "Small error" , "Mistake, blunder" .)