Notice a split coming (6)

I believe the answer is:

advent

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'coming' is the definition.
(advent is the arrival or coming of something)

'notice a split' is the wordplay.
'notice' becomes 'ad' (short for advert).
'a split' becomes 'vent' (I can't explain this - if you can you should believe this answer much more).
'ad'+'vent'='ADVENT'

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(Other definitions for advent that I've seen before include "Christmas shopping time in" , "when the Christmas shopping has to be done?" , "Pre-Christmas season for Christians" , "Season for a candle?" , "Second Coming" .)

I've seen this clue in The Globe and Mail.

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