Back-dated a leave? (3)

I believe the answer is:

ago

I'm a little stuck... Click here to teach me more about this clue!

This clue could be a double definition.

'back' is the first definition.
('years back' means 'years ago')

'dated a leave?' is the second definition.
'ago' can be an answer for 'dated' (thesaurus). I am not certain of the 'a leave?' bit.

Can you help me to learn more?

(Other definitions for ago that I've seen before include "(Years) before the present time" , "Back (in time)" , "Earlier, gone by" , "Time past" , "Previously" .)

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

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