All that is acceptable in revolutionary rhyme (8)
I believe the answer is:
universe
'all that is' is the definition.
(I've seen this before)
'acceptable in revolutionary rhyme' is the wordplay.
'acceptable' becomes 'u' ((Film classification)).
'revolutionary' shows that the letters should be reversed in order.
'rhyme' becomes 'verse' ('verse' can be a synonym of 'rhyme'**).
'in' in reverse letter order is 'ni'.
'u'+'ni'+'verse'='UNIVERSE'
(Other definitions for universe that I've seen before include "The whole of creation" , "sphere of activity" , "The totality of matter, energy and space" , "all we know?" , "Edible crustacean" .)