Ambassador's neglect during bad year (8)
I believe the answer is:
emissary
'ambassador's' is the definition.
(thesaurus)
'neglect during bad year' is the wordplay.
'neglect' becomes 'miss' (missing is a kind of neglecting).
'during' is an insertion indicator.
'bad' indicates anagramming the letters.
'year' with letters rearranged gives 'eary'.
'miss' placed within 'eary' is 'EMISSARY'.
(Other definitions for emissary that I've seen before include "Messenger, envoy" , "Diplomat sent on special task" , "Government messenger" , "Delegate" , "Diplomatic agent" .)