Important date in October added (3)

I believe the answer is:

era

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

'in october added' is the wordplay.
'in' indicates a hidden word.
'ERA' can be found hidden inside 'october added'.

(Other definitions for era that I've seen before include "Epoch, period" , "Specific time" , "Important time" , "Period, age" , "Major division of geological time" .)

I've seen this clue in The Times.

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