Gibbon, for one, a senior cleric (7)
I believe the answer is:
primate
I believe this is a double definition.
'gibbon for one' is the first definition.
(gibbon is a kind of primate)
'a senior cleric' is the second definition.
(I've seen this before)
(Other definitions for primate that I've seen before include "Chief bishop" , "Capuchin could be such" , "Bishop; large mammal" , "E.g. monkey, ape, archbishop" , "C of E archbishop" .)