Refuse, refute (4)
I believe the answer is:
deny
This clue is a double definition.
'refuse' is the first definition.
(I know that deny is a kind of keep back)
'refute' is the second definition.
(I've seen this before)
(Other definitions for deny that I've seen before include "Claim to be untrue" , "Disown" , "Refuse to acknowledge" , "Refuse access to" , "Refute, contradict" .)