Big primates (4)
I believe the answer is:
apes
'big primates' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for apes that I've seen before include "Imitates like primates" , "Species of primate" , "Peas (anag)" , "Parrots" , "Imitates in every aspect" .)