Below zero (5)
I believe the answer is:
minus
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">below zero</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 minus that I've seen before include "Negative arithmetic operation" , "Disadvantage" , "Less, without" , "Lacking; below zero" , "Reduced by the subtraction of - thus?" .)