Eldest child originally rootless, out to take revenge (6,3,6)

I believe the answer is:

settle old scores

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'take revenge' is the definition.
I know nothing about this answer so I can't judge whether this works.

'eldest child originally rootless out' is the wordplay.
'originally' suggests taking the first letters.
'out' indicates anagramming the letters (out can mean wrong or inaccurate).
The initial letter of 'child' is 'c'.
'eldest'+'c'+'rootless'='eldestcrootless'
'eldestcrootless' anagrammed gives 'SETTLE OLD SCORES'.

'to' is the link.

Can you help me to learn more?

(Other definitions for settle old scores that I've seen before include "Get even" , "Deal with historical complaints" .)

I've seen this clue in The Times.

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