Briefly ring reviewer Mark (9)
I believe the answer is:
diacritic
'mark' is the definition.
(diacritic is a kind of mark)
'briefly ring reviewer' is the wordplay.
'briefly' means to remove the last letter.
'ring' becomes 'dial' (I've seen this before).
'reviewer' becomes 'critic' (I've seen this before).
'dial' with its final letter taken off is 'dia'.
'dia'+'critic'='DIACRITIC'
(Other definitions for diacritic that I've seen before include "Mark" , "one showing a pronounced difference" , "accent, for example" , "[ACCENT] , perhaps" , "grave perhaps" .)