Ape or primate? One's uncertain (11)
I believe the answer is:
impersonate
'ape' is the definition.
(thesaurus)
'primate? one's uncertain' is the wordplay.
'uncertain' is an anagram indicator.
'primate'+'ones'='primateones'
'primateones' with letters rearranged gives 'IMPERSONATE'.
'or' acts as a link.
(Other definitions for impersonate that I've seen before include "ape" , "Mimic" , "Copy" , "Pinch identity of" , "to be an impressionist" .)