Sort of bun devoured but not defeated (8)
I believe the answer is:
unbeaten
'not defeated' is the definition.
(I've seen this before)
'sort of bun devoured' is the wordplay.
'sort of' indicates an anagram.
'devoured' becomes 'eaten' (similar in meaning).
'bun' is an anagram of 'unb'.
'unb'+'eaten'='UNBEATEN'
'but' is the link.
(Other definitions for unbeaten that I've seen before include "not having suffered defeat" , "having at worst drawn badly?" , "Undefeated" , "Not punished" , "Not conquered" .)