Most opulent revolutionary is in stir, oddly (7)
I believe the answer is:
richest
'most opulent' is the definition.
('rich' can be similar in meaning to 'opulent')
'revolutionary is in stir oddly' is the wordplay.
'revolutionary' becomes 'Che' (Che Guevara the Marxist revolutionary).
'is in' is an insertion indicator.
'oddly' is an anagram indicator (letters in an odd order).
'stir' anagrammed gives 'rist'.
'che' put into 'rist' is 'RICHEST'.
(Other definitions for richest that I've seen before include "Least likely to be a beggar" , "Wealthiest" , "extremely ornate" , "Most productive" , "Having the most, money say" .)