Revolutionary claim about compound (8)
I believe the answer is:
chemical
'compound' is the definition.
(synonyms)
'revolutionary claim about' is the wordplay.
'revolutionary' becomes 'Che' (Che Guevara the Marxist revolutionary).
'about' indicates anagramming the letters.
'claim' with letters rearranged gives 'mical'.
'che'+'mical'='CHEMICAL'
(Other definitions for chemical that I've seen before include "Artificial compound" , "Laboratory substance" , "Chic male (anag.)" , "Of the interactions of substances" , "Material produced by a reaction involving changes in atoms or molecules" .)