Deny or refuse to acknowledge (8)
I believe the answer is:
disclaim
This clue is a double definition.
'deny' is the first definition.
(I know that disclaim is a more specific form of deny)
'refuse to acknowledge' is the second definition.
(I've seen this before)
(Other definitions for disclaim that I've seen before include "Deny, refuse to acknowledge" , "Forswear" , "Renounce" , "Disown or deny, maybe responsibility" , "Deny or relinquish" .)