Accompanying cool revolutionary in charge of chopper (10)
I believe the answer is:
incidental
'accompanying' is the definition.
(I know that accompanying can be written as incidental)
'cool revolutionary in charge of chopper' is the wordplay.
'cool' becomes 'in' ('in' can mean fashionable or cool).
'revolutionary' says the letters should be written in reverse (letters revolve around).
'in charge' becomes 'ic' (abbreviation for 'in charge').
'of chopper' becomes 'dental' (relating to teeth - teeth chop things).
'ic' backwards is 'ci'.
'in'+'ci'+'dental'='INCIDENTAL'
(Other definitions for incidental that I've seen before include "By the way" , "Not an essential" , "form of music" , "fortuitous" .)