"What are we waiting for?" (4,2)
I believe the answer is:
lets go
'what are we waiting for?' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for lets go that I've seen before include "Come on then, we're off!" , "Releases from one's grip" , "fires" , "Liberates" , "Order to leave" .)