Long to be a revolutionary (4)
I believe the answer is:
ache
'long to' is the definition.
(thesaurus)
'a revolutionary' is the wordplay.
'revolutionary' becomes 'che' (Che Guevara the Marxist revolutionary).
'a'+'che'='ACHE'
'be' is the link.
(Other definitions for ache that I've seen before include "Dull throbbing pain" , "Feel sore" , "Play up" , "Each (anag.)" , "Hanker" .)