With the least delay (7)
I believe the answer is:
soonest
'with the least delay' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for soonest that I've seen before include "'Least said, ... mended (7)'" , "First" , "At the earliest time" , "As early as possible" , "Most readily" .)