Do dine with a companion (5)
I believe the answer is:
cheat
'do' is the definition.
(I've seen this before)
'dine with a companion' is the wordplay.
'dine' becomes 'eat' (I've seen this before).
'with' means one lot of letters go next to another.
'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" .)