Joined the club (6)

I believe the answer is:

united

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'joined' is the definition.
(synonyms)

I don't understand the rest of the clue.

(Other definitions for united that I've seen before include "Untied (anag.)" , "Joined together -- in duet (anag)" , "Manchester _____, current Premiership champions with..." , "Joined together as one" , "Joined - football club" .)

I've seen this clue in the Evening Standard.

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