Memo directive (4)
I believe the answer is:
asap
'memo directive' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for asap that I've seen before include "As soon as possible (abbrev.)" , "Initials notation meaning with all possible speed" , "Notation-acronym meaning without delay" , "'As quickly as you can, initially (4)'" , "Notation for urgent, quick as you can (4)" .)