Maestro out to cage minute monkey (8)
I believe the answer is:
marmoset
'monkey' is the definition.
(I know that marmoset is a type of New World monkey)
'maestro out to cage minute' is the wordplay.
'out' indicates an anagram (out can mean wrong or inaccurate).
'to cage' is an insertion indicator (inserted letters are locked up).
'minute' becomes 'm' (abbreviation).
'maestro' with letters rearranged gives 'maroset'.
'maroset' enclosing 'm' is 'MARMOSET'.
(Other definitions for marmoset that I've seen before include "Small New World monkey" , "Star memo about kind of monkey" , "Small South American monkey" , "Primate" , "Small tropical American monkey" .)