Refuse permission to examine ring (4)
I believe the answer is:
veto
'refuse permission' is the definition.
(I've seen this before)
'examine ring' is the wordplay.
'examine' becomes 'vet' (I've seen this before).
'ring' becomes 'o'.
'vet'+'o'='VETO'
'to' acts as a link.
(Other definitions for veto that I've seen before include "black ball" , "Refuse to authorise" , "Rule out" , "A confused vote, altogether negative" , "Don't allow" .)