PDQ (4)
I believe the answer is:
asap
'pdq' 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 "Notation meaning with minimum delay" , "Notation or acronym meaning without avoidable delay" , "Notation for urgent, quick as you can (4)" , "Notation for as quickly as you can" , "At the earliest opportunity (abbrev.)" .)