Falter as revolutionary losing heart (4)
I believe the answer is:
reel
'falter' is the definition.
(thesaurus)
'revolutionary losing heart' is the wordplay.
'revolutionary' becomes 'rebel' (rebel is a kind of revolutionary).
'losing heart' says to hollow out the word (remove centre letters).
'rebel' with its centre taken out is 'REEL'.
'as' acts as a link.
(Other definitions for reel that I've seen before include "Dance - sway - cotton holder" , "Wind" , "Turn around in the dance" , "Part of film; dance" , "Stagger about in lively dance" .)