Umpteenth (3)
I believe the answer is:
nth
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">umpteenth</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 nth that I've seen before include "To the -- degree" , "Umpteenth" .)