About to screen Oliver Stone film about President Grant (3)
I believe the answer is:
own
'grant' is the definition.
(thesaurus)
'about to screen oliver stone film about president' is the wordplay.
'about' becomes 'on'.
'to screen' indicates putting letters inside.
'oliver stone film about president' becomes 'w' (W, film about George W Bush).
'on' enclosing 'w' is 'OWN'.
(Other definitions for own that I've seen before include "Have in one's possession" , "Allow" , "Possess - recognise - admit" , "Private" , "Be in legal possession of (3)" .)