Big baboon (8)
I believe the answer is:
mandrill
'big baboon' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for mandrill that I've seen before include "African baboon with red and blue muzzle and hindquarters" , "Colourful baboon in the damn rill" , "Large baboon" , "Ape" , "West African baboon-like primate" .)