Joined in duet with variations (6)

I believe the answer is:

united

I'm a little stuck... Click here to teach me more about this clue!

'joined' is the definition.
(I know that joined can be written as united)

'in duet with variations' is the wordplay.
'in duet' can be anagrammed to 'UNITED'.
But, I'm not clear how the anagram is indicated.

Can you help me to learn more?

(Other definitions for united that I've seen before include "Joined together as in alliance" , "Joined together as one" , "cooperative" , "See 14" , "See 9" .)

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