Has grown strangely partial (4)
I believe the answer is:
owns
'has' is the definition.
('own' can be a synonym of 'have')
'grown strangely partial' is the wordplay.
'partial' indicates a hidden word.
'OWNS' is hidden within 'grown strangely'.
(Other definitions for owns that I've seen before include "Confesses" , "Possesses" , "Belongs to" , "uses" , "Admits possession" .)