E in QED (4)
I believe the answer is:
erat
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">e in qed</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for erat that I've seen before include "Quod - - demonstrandum (QED)" , "The E of QED" .)