Tom is a violent Communist (6)
I believe the answer is:
maoist
'communist' is the definition.
(thesaurus)
'tom is a violent' is the wordplay.
'violent' is an anagram indicator (I've seen this in other clues).
'tom'+'is'+'a'='tomisa'
'tomisa' with letters rearranged gives 'MAOIST'.
(Other definitions for maoist that I've seen before include "Devotee once of the little red book" , "Political ideologist" , "Chinese communist" , "Supporter of a previous Chinese leader" , "supporter of old Communist" .)