Kind of monkey (6)
I believe the answer is:
rhesus
'kind of monkey' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for rhesus that I've seen before include "Type of macaque" , "Usually a positive factor in man" , "Type of monkey and blood category" , "King, in Greek mythology" , "Kind of monkey or blood group" .)