Article about the setter's revolutionary nom de guerre (6)
I believe the answer is:
anonym
'nom de guerre' is the definition.
(synonyms)
'article about the setter's revolutionary' is the wordplay.
'article' becomes 'an' (English indefinite article).
'about' becomes 'on' (as in a book 'on' a certain topic).
'the setter's' becomes 'my' (belonging to the crossword setter).
'revolutionary' says the letters should be written in reverse (letters revolve around).
'my' reversed gives 'ym'.
'an'+'on'+'ym'='ANONYM'
(Other definitions for anonym that I've seen before include "Pseudonym" , "Person whose name is not given" , "Fictitious name" , "Assumed or false name" , "One whose name is not given" .)