Offender’s supper finally eaten by chef (5)
I believe the answer is:
crook
'offender's' is the definition.
(crook is a kind of offender)
'supper finally eaten by chef' is the wordplay.
'finally' suggests the final letters.
'eaten by' means one lot of letters goes inside another.
'chef' becomes 'cook' (I've seen this before).
The final letter of 'supper' is 'r'.
'r' inserted within 'cook' is 'CROOK'.
(Other definitions for crook that I've seen before include "Professional criminal" , "Shepherd's staff" , "Hooked staff" , "Swindler - crosier - ill (in Australia)" , "Something kinky" .)