Refuse to acknowledge study, say, in the end (4)
I believe the answer is:
deny
'refuse to acknowledge' is the definition.
(I've seen this before)
'study say in the end' is the wordplay.
'study' becomes 'den' (I've seen this before).
'in the end' suggests the final letters.
The last letter of 'say' is 'y'.
'den'+'y'='DENY'
(Other definitions for deny that I've seen before include "Refuse access to" , "Refuse to accept" , "Abnegate" , "Claim to be untrue" , "Declare untrue" .)