A month in a tribal division (4)

I believe the answer is:

sept

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This might be a double definition.

'a month' is the first definition.
(Sept is an example)

'a tribal division' is the second definition.
'sept' can be an answer for 'division' (thesaurus). I am unsure of the 'a tribal' bit.

'in' is the link.

Can you help me to learn more?

(Other definitions for sept that I've seen before include "Part of clan" , "Branch of Irish clan" , "Thirty days" , "Division of a tribe in Ireland or Scotland" , "Short month" .)

I've seen this clue in the Sydney Morning Herald.

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