Genuine amateur theatre's somewhat revolutionary (4)
I believe the answer is:
true
'genuine' is the definition.
(associated in meaning)
'amateur theatre's somewhat revolutionary' is the wordplay.
'somewhat' indicates a hidden word.
'revolutionary' says the letters should be written backwards (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" .)