Vetoed attempt in favouring study (9)
I believe the answer is:
forbidden
'vetoed' is the definition.
(thesaurus)
'attempt in favouring study' is the wordplay.
'attempt' becomes 'bid' (bid is a kind of attempt).
'in' indicates putting letters inside.
'favouring' becomes 'for' (I've seen this before).
'study' becomes 'den' (I've seen this before).
'for'+'den'='forden'
'bid' placed within 'forden' is 'FORBIDDEN'.
(Other definitions for forbidden that I've seen before include "Proscribed" , "Illicit pleasure" , "Disallowed, banned" , "not 35 [PERMISSIBLE]" , "Not allowed, banned" .)