Opening night (8)
I believe the answer is:
premiere
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">opening night</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 premiere that I've seen before include "Opening performance" , "significant performance" , "First show" , "First public performance of a play or movie" , "First screening" .)