Group inch aboard craft, an old chopper (10)
I believe the answer is:
guillotine
'an old chopper' is the definition.
(old-fashioned device for chopping heads off)
'group inch aboard craft' is the wordplay.
'group' becomes 'lot'.
'inch' becomes 'in' (abbreviation).
'aboard' means one lot of letters goes inside another.
'craft' becomes 'guile' (synonyms).
'lot'+'in'='lotin'
'lotin' placed into 'guile' is 'GUILLOTINE'.
(Other definitions for guillotine that I've seen before include "move to curtail debate" , "Beheading machine" , "One with sharp blade" , "Machine for cutting paper (or French aristocrats) down to size" , "revolutionary chopper" .)