Concluding, on posting the second off (6)

I believe the answer is:

ending

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'concluding' is the definition.
(I've seen this before)

I cannot understand how the remainder of the clue works.

(Other definitions for ending that I've seen before include "Cessation" , "Bringing to a close" , "Coda" , "terminal" , "Gin den (anag.)" .)

I've seen this clue in the Evening Standard.

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