Simultaneous (10)
I believe the answer is:
coincident
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">simultaneous</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I know that simultaneous can be written as coincident)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for coincident that I've seen before include "Matching" , "Occurring together" , "in the same place" .)