Alienate (8)
I believe the answer is:
estrange
'alienate' is the definition.
(I know that alienate can be written as estrange)
This is all the clue.
(Other definitions for estrange that I've seen before include "Anger set (anag.)" , "As Regent (anag.)" , "Lose friendship" , "Reagents (anag.)" , "disunity" .)