Adult female, strong and stable witness (6)

I believe the answer is:

affirm

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'stable witness' is the definition.
'affirm' can be an answer for 'witness' (thesaurus). I'm not sure about the 'stable' bit.

'adult female strong' is the wordplay.
'adult' becomes 'a' (abbreviation).
'female' becomes 'f' (common abbreviation).
'strong' becomes 'firm' (synonyms).
'a'+'f'+'firm'='AFFIRM'

'and' is the link.

Can you help me to learn more?

(Other definitions for affirm that I've seen before include "Publicly state" , "Maintain" , "Declare one's commitment (to)" , "State as a fact, assert" , "Assert, avow" .)

I've seen this clue in the Independent.

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