Enterprising (2-5)
I believe the answer is:
go-ahead
'enterprising' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for go-ahead that I've seen before include "Up-and-coming - authorisation" , "Enterprisingly progressive" , "Enterprising" , "Pioneering (green light?)" , "Permission to proceed" .)