One revolutionary can be a pain (4)
I believe the answer is:
ache
'be a pain' is the definition.
(I've seen this before)
'one revolutionary' is the wordplay.
'one' becomes 'a'.
'revolutionary' becomes 'che' (Che Guevara the Marxist revolutionary).
'a'+'che'='ACHE'
'can' is the link.
(Other definitions for ache that I've seen before include "Feel sore" , "strong feeling" , "Nagging pain" , "Similar" , "yearning" .)