Passé mood duet to be reworked (8)
I believe the answer is:
outmoded
'passe' is the definition.
(synonyms)
'mood duet to be reworked' is the wordplay.
'to be reworked' indicates anagramming the letters.
'mood'+'duet'='moodduet'
'moodduet' anagrammed gives 'OUTMODED'.
(Other definitions for outmoded that I've seen before include "Old-fashioned" , "No longer in fashion" , "Dated" , "No longer fashionable" .)