Primate in cloak, heading off (3)
I believe the answer is:
ape
'primate' is the definition.
(I've seen this before)
'cloak heading off' is the wordplay.
'cloak' becomes 'cape' (cape is a kind of cloak).
'heading off' means to remove the first letter.
'cape' with its initial letter taken away is 'APE'.
'in' acts as a link.
(Other definitions for ape that I've seen before include "Send up" , "Copy - primate" , "Imitate like primate" , "Closely follow" , "Simulate" .)