Divisor (11)
I believe the answer is:
denominator
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">divisor</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 denominator that I've seen before include "Lower half of fraction (could be common!)" , "Lower number" , "Divisor" , "what's under the line?" .)