Genuine amateur theatre's somewhat revolutionary (4)
I believe the answer is:
true
'genuine' is the definition.
(synonyms)
'amateur theatre's somewhat revolutionary' is the wordplay.
'somewhat' indicates a hidden word.
'revolutionary' shows that the letters should be reversed in order (letters revolve around).
'eurt' is hidden within 'amateur theatres'.
'eurt' written backwards gives 'TRUE'.
(Other definitions for true that I've seen before include "Genuine; faithful" , "to be believed?" , "Supported by the facts" , "Exact, factual" , "Genuine, real" .)