Fast direction out of city (6)
I believe the answer is:
presto
'fast' is the definition.
(musical instruction)
'direction out of city' is the wordplay.
I cannot really understand how this works, but
'direction' could be 's' (S is an example) and 's' is found in the answer.
'of' could be 'o' and 'o' is found in the answer.
The remaining letters 'pret' is a valid word which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).
(Other definitions for presto that I've seen before include "hey......,cries the magician" , "Hey, quickly for a magician" , "Hey ..., according to the magician" , "(In music) fast" , "at great speed..." .)