Grim aunt possibly becoming mellow (8)

I believe the answer is:

maturing

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'becoming mellow' is the definition.
I can't judge whether this definition defines the answer.

'grim aunt possibly' is the wordplay.
'possibly' indicates anagramming the letters.
'grim'+'aunt'='grimaunt'
'grimaunt' is an anagram of 'MATURING'.

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(Other definitions for maturing that I've seen before include "Growing ripe or developing" , "Growing ripe, reaching full growth" , "Growing, ripening" .)

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