Feeling contrite about calamity? Good! (5)

I believe the answer is:

ruing

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'feeling contrite' is the definition.
(I've seen this in another clue)

'calamity? good' is the wordplay.
'calamity?' becomes 'ruin' (I can't justify this - if you can you should give a lot more credence to this answer).
'good' becomes 'g' (abbreviation).
'ruin'+'g'='RUING'

'about' is the link.

Can you help me to learn more?

(Other definitions for ruing that I've seen before include "Feeling bad" , "Regretful" , "full of remorse?" , "Bitterly regretting" , "Feeling sorry for" .)

I've seen this clue in The Guardian.

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