Joined in duet maybe (6)
I believe the answer is:
united
'joined' is the definition.
(I've seen this before)
'in duet maybe' is the wordplay.
'maybe' indicates anagramming the letters.
'in'+'duet'='induet'
'induet' is an anagram of 'UNITED'.
(Other definitions for united that I've seen before include "Merged into one" , "collective" , "See 9" , "Allied or combined" , "Football team" .)