Long-armed ape (9)
(Other definitions for orangutan that I've seen before include "a big sub-human creature" , "ape" , "Primate" .)
'long-armed ape' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for gibbon that I've seen before include "A historian; SE Asian forest creature" , "an eighteenth-century author" , "Large tailless ape" , "Small ape - famous historian" , "Member of the ape family" .)