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