Instantly (2,1,5)
'instantly' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for at once that I've seen before include "'Immediately (2,4)'" , "Instantly" , "right away" , "Octane (anag)" , "from the kick-off" .)
'instantly' is the definition.
(synonyms)
This is the entire clue.
(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" .)