Monkey keeping bull close (9)
I believe the answer is:
proximate
'close' is the definition.
(similar in meaning)
'monkey keeping bull' is the wordplay.
'monkey' becomes 'primate' (I've seen this before).
'keeping' indicates putting letters inside (some letters kept inside).
'bull' becomes 'ox'.
'primate' placed around 'ox' is 'PROXIMATE'.
(Other definitions for proximate that I've seen before include "next door" , "Very close" , "Closest" , "immediately following" .)