Start of a reminiscence (4)
I believe the answer is:
once
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">start of a reminiscence</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 once that I've seen before include "One-time musical film and song" , "Long ago" , "not repeatedly" , "On a single (or past) occasion" , "in bygone days" .)