Group of musicians -- a chorister's lost without one (9)

I believe the answer is:

orchestra

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'group of musicians' is the definition.
(I've seen this before)

I can't explain the remainder of the clue.

(Other definitions for orchestra that I've seen before include "bandsmen?" , "Assembly of musicians as in pit" , "Ensemble of players" , "Musicians, maybe in theatre" , "many players" .)

I've seen this clue in The Telegraph.

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