Shot cad harbours zero bitterness (7)

I believe the answer is:

rancour

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'bitterness' is the definition.
(I know that bitterness can be written as rancour)

'shot cad harbours zero' is the wordplay.
'shot' becomes 'ran' (I can't explain this - if you can you should give a lot more credence to this answer).
'cad' becomes 'cur' (I've seen this in another clue).
'harbours' is an insertion indicator.
'zero' becomes 'O' (O resembles 0).
'cur' going around 'o' is 'cour'.
'ran'+'cour'='RANCOUR'

Can you help me to learn more?

(Other definitions for rancour that I've seen before include "Antipathy" , "Deep-seated hostility" , "Long-lasting bitterness" , "Malice" , "Deep, bitter hate" .)

I've seen this clue in The Daily Express.

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