Muses get a Stoic in trouble (9)
I believe the answer is:
cogitates
'muses' is the definition.
(cogitating is a kind of musing)
'get a stoic in trouble' is the wordplay.
'in trouble' indicates an anagram.
'get'+'a'+'stoic'='getastoic'
'getastoic' anagrammed gives 'COGITATES'.
(Other definitions for cogitates that I've seen before include "Muses" , "Thinks deeply" , "Ponders" .)