Crossword Genius

Going off grit, not used (7)

Ross

I believe the answer is:

rotting

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'going off' is the definition.
The answer and definition can be both related to change as well as being present participle verbs.
Perhaps there's an association between them I don't understand?

'grit not used' is the wordplay.
'used' indicates an anagram.
'grit'+'not'='gritnot'
'gritnot' anagrammed gives 'ROTTING'.

Can you help me to learn more?

(Other definitions for rotting that I've seen before include "Sultanate in NW Borneo" , "Decaying" , "corruption?" , "Putrid" , "Going bad" .)

I've seen this clue in The Mirror.
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