Irregularity (7)
I believe the answer is:
anomaly
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">irregularity</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 anomaly that I've seen before include "Special case" , "Deviation from the norm or expected" , "Irregularity or inconsistency, deviation from norm" , "eccentricity" , "irregular feature" .)