Before November, get leader to leave band (5)

I believe the answer is:

octet

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'band' is the definition.
(I know that octet is a type of band)

I don't understand the rest of the clue.

(Other definitions for octet that I've seen before include "Music for eight" , "A group of eight instruments or voices" , "Set of eight" , "Musical group" , "Medieval Latin hymn" .)

I've seen this clue in The Irish Times.

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