Deprive of energy (8)
I believe the answer is:
enervate
'deprive of energy' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for enervate that I've seen before include "Make drained of energy" , "Unnerve, unsettle" , "Spiritless" , "Make weak" , "Take strength from" .)