One joins them in song (6)

I believe the answer is:

anthem

'song' is the definition.
(anthem is a kind of song)

'one joins them' is the wordplay.
'one' becomes 'an' (an apple is one apple).
'joins' is a charade indicator (letters next to each other).
'an'+'them'='ANTHEM'

'in' acts as a link.

(Other definitions for anthem that I've seen before include "Uplifting song -- the man (anag)" , "Song of praise or loyalty" , "The man for a rousing song" , "National tune" , "National hymn" .)

I've seen this clue in the Evening Standard.

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