Arm revolutionary centre in seizure (3)
I believe the answer is:
uzi
'arm' is the definition.
(type of gun)
'revolutionary centre in seizure' is the wordplay.
'revolutionary' says the letters should be written in reverse.
'centre in' means to look at the middle letters.
The middle of 'seizure' is 'izu'.
'izu' back-to-front is 'UZI'.
(Other definitions for uzi that I've seen before include "Type of submachine gun" , "Israeli-designed sub-machine gun" , "killer" , "Submachine-gun" , "Israeli sub-machine gun" .)