Gave power to English knight, one that's exhausted (7)
I believe the answer is:
enabled
'gave power to' is the definition.
(I've seen this in another clue)
'english knight one that's exhausted' is the wordplay.
'english' becomes 'e' (abbreviation).
'knight' becomes 'N' (chess abbreviation).
'one' becomes 'a' (a thing is one thing).
'that's exhausted' becomes 'bled' (to exhaust something might be to bleed it dry).
'e'+'n'+'a'+'bled'='ENABLED'
(Other definitions for enabled that I've seen before include "Qualified" , "Be laden (anag.)" , "Made possible, facilitated" , "Facilitated or empowered" , "Allowed" .)