Slip or sin (5)
I believe the answer is:
lapse
<span class="explanation-format__ClueExplanation">This clue is a double definition.<br/ ><br/ >'<span class="explanation-format__original">slip</span>' is the first definition.<br/ ><span class="explanation-format__explanation">(I know that lapse is a more specific form of the action slip)</span><br/ ><br/ >'<span class="explanation-format__original">sin</span>' is the second definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ ></span>
(Other definitions for lapse that I've seen before include "Decline into an inferior state" , "Slight error as caused by inattention" , "Brief failure (of concentration)" , "Loss (in concentration, say?)" , "Momentary mistake" .)