Study your initial decline (4)
I believe the answer is:
deny
'decline' is the definition.
(thesaurus)
'study your initial' is the wordplay.
'study' becomes 'den' (term for a study or office).
'initial' suggests taking the first letters.
The first letter of 'your' is 'y'.
'den'+'y'='DENY'
(Other definitions for deny that I've seen before include "Declare not to be true" , "Forbid; not agree" , "Forbid; contradict" , "Declare non-existent" , "Refute, contradict" .)