Waiting in ambush (7)
I believe the answer is:
lurking
'waiting in ambush' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for lurking that I've seen before include "Lying hidden in ambush" , "In hiding for ambush" , "Waiting in ambush" , "Lying in wait, ready to ambush perhaps" , "Skulking" .)