Type of monkey and a blood component (6)
I believe the answer is:
rhesus
'type of monkey and a blood component' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for rhesus that I've seen before include "Primate" , "Blood type or sort of monkey" , "Type of monkey and blood category" , "(Kind of monkey) used in medical experiments" , "Asian monkey - blood factor" .)