Defeated, having dined on a piece of bread (6)
I believe the answer is:
beaten
'defeated' is the definition.
('beat' can be a synonym of 'defeat')
'dined on a piece of bread' is the wordplay.
'dined' becomes 'eaten' (having had a meal).
'on' means one lot of letters go next to another.
'a piece of' indicates taking the first letters.
The first letter of 'bread' is 'b'.
'eaten' put after 'b' is 'BEATEN'.
'having' is the link.
(Other definitions for beaten that I've seen before include "Baffled" , "Defeated - whipped" , "Vanquished" , "Failed to win - punished" , "Worsted" .)