Backdated a leave? (3)

I believe the answer is:

ago

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'backdated' is the definition.
The answer and definition are different parts of speech. However, past participle verbs and adjectives occasionally define each other.

'a leave?' is the wordplay.
'leave?' becomes 'go' (to go is to depart or leave).
'a'+'go'='AGO'

Can you help me to learn more?

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

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

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