No revolutionary dresses in identical shirts (7)
I believe the answer is:
tsarist
'no revolutionary' is the definition.
(tsarists opposed the Russian Revolution)
'dresses in identical shirts' is the wordplay.
'dresses' becomes 'saris' (sari is a kind of dress).
'in' is an insertion indicator.
'identical shirts' becomes 'TT' (two T's, as in T-shirts).
'saris' inserted inside 'tt' is 'TSARIST'.
(Other definitions for tsarist that I've seen before include "Artists (anag.); supporter of Russian emperor" , "Russian royalist" , "Russian monarchist" , "Supporter of the Russian Empire" , "Like Russia once" .)