Instantly (2,1,5)
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">instantly</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 at once that I've seen before include "'Immediately (2,4)'" , "Instantly" , "right away" , "Octane (anag)" , "from the kick-off" .)
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">instantly</span>' is the definition.<br/ ><span class="explanation-format__explanation">(synonyms)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for in a flash that I've seen before include "Instantly, straightaway" , "How lightning appears" , "pictures may be taken" , "Where American detected electricity" , "Almost instantly" .)