Something to keep aunty in change! (7)

I believe the answer is:

annuity

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'something to keep' is the definition.
I can't tell whether this defines the answer.

'aunty in change' is the wordplay.
'change' indicates anagramming the letters.
'aunty'+'in'='auntyin'
'auntyin' anagrammed gives 'ANNUITY'.

Can you help me to learn more?

(Other definitions for annuity that I've seen before include "Form of investment" , "guaranteed payment" , "Sum paid yearly" , "Regular income from a fund" , "Pension income" .)

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

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