Spare key, yours some time ago? (5)

I believe the answer is:

thine

'yours some time ago?' is the definition.
(historic form of 'yours')

'spare key' is the wordplay.
'spare' becomes 'thin' ('thin' can be similar in meaning to 'spare').
'key' becomes 'e' (I've seen this in other clues**).
'thin'+'e'='THINE'

(Another definition for thine that I've seen is " Yours (archaic)".)

I've seen this clue in The Times.

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