Flog small company on impulse (7)
I believe the answer is:
scourge
'flog' is the definition.
(I've seen this before)
'small company on impulse' is the wordplay.
'small' becomes 's' (abbreviation - e.g. clothes size).
'company' becomes 'co' (abbreviation).
'on' means one lot of letters go next to another.
'impulse' becomes 'urge' ('urge' can be a synonym of 'impulse').
's'+'co'+'urge'='SCOURGE'
(Other definitions for scourge that I've seen before include "menace" , "Harass" , "One providing lashings" , "Cause great suffering to (someone); whip" , "Bane, curse" .)