"Right away" letters (4)
I believe the answer is:
asap
'right away letters' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for asap that I've seen before include "Notation meaning with minimum delay" , "Notation or acronym meaning without avoidable delay" , "Notation meaning without delay, treat as urgent" , "'At the earliest moment, initially (4)'" , "Initials notation meaning with all possible speed" .)