Working after noon and feeling rubbish (8)
I believe the answer is:
nonsense
'rubbish' is the definition.
(thesaurus)
'working after noon and feeling' is the wordplay.
'working' becomes 'on'.
'after' means one lot of letters go next to another.
'noon' becomes 'n'.
'and' is a charade indicator (letters next to each other).
'feeling' becomes 'sense' (I've seen this before).
'on' put after 'n' is 'non'.
'non'+'sense'='NONSENSE'
(Other definitions for nonsense that I've seen before include "Quick look" , "Foolish or meaningless words" , "Rubbish, drivel" , "Rubbish, rot" , "Bunk" .)