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' is an anagram indicator.
'devoured' becomes 'eaten' (similar in meaning).
'bun' with letters rearranged gives 'unb'.
'unb'+'eaten'='UNBEATEN'
'but' acts as a 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" .)