A bit of business returning on the Met line (4)

I believe the answer is:

item

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'a bit' is the definition.
(I have seen 'Bit of news' mean 'item' so perhaps 'bit' could also mean 'item')

I don't understand how the rest of the clue works.

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(Other definitions for item that I've seen before include "See couple" , "Individual thing" , "couple making out {TIME}..." , "newspaper article" , "Indivual unit" .)

I've seen this clue in the Evening Standard.

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