Do dine with a companion (5)
I believe the answer is:
cheat
'do' is the definition.
(do can mean to cheat or defraud)
'dine with a companion' is the wordplay.
'dine' becomes 'eat' (eat a meal).
'with' is a charade indicator (letters next to each other).
'a companion' becomes 'ch' (Companion of Honour).
'eat' after 'ch' is 'CHEAT'.
(Other definitions for cheat that I've seen before include "One dealing dishonestly" , "Con" , "rook" , "Act unfairly (in game)" , "Compete dishonestly" .)