Prelude to an opera (8)
I believe the answer is:
overture
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">prelude to an opera</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for overture that I've seen before include "Orchestral introduction to an opera" , "Introduction to, eg, an opera" , "Instrumental prelude" , "10 {COMPOSITION]" , "offer" .)