$1000 before noon for old matriarch (7)

I believe the answer is:

grandam

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'old matriarch' is the definition.
The definition suggests a singular noun which matches the answer.

'$1000 before noon' is the wordplay.
'$1000' becomes 'grand' (I've seen this in another clue).
'before noon' becomes 'AM' (as in AM on a clock).
'grand'+'am'='GRANDAM'

'for' acts as a link.

Can you help me to learn more?

(Another definition for grandam that I've seen is " Experienced old woman".)

I've seen this clue in The Times.

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