Alienate new sergeant (8)
I believe the answer is:
estrange
'alienate' is the definition.
('estrange' can be a synonym of 'alienate')
'new sergeant' is the wordplay.
'new' indicates an anagram.
'sergeant' is an anagram of 'ESTRANGE'.
(Other definitions for estrange that I've seen before include "Ten gears (anag.)" , "Cause to be alienated" , "Get cut off" , "Antagonise using reagents" , "Alienate -- sergeant (anag)" .)