Crossword Genius

Potentially one’s best friend (5)

Ross

I believe the answer is:

china

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'friend' is the definition.
(cockney rhyming slang, mate is china plate)

'potentially one's best' is the wordplay.
'potentially one' becomes 'chin' (I am not sure about this - if you are sure you should believe this answer much more).
'best' becomes 'a'.
'chin'+'a'='CHINA'

Can you help me to learn more?

(Other definitions for china that I've seen before include "friend or companion" , "Large country; mate" , "Ceramic; country" , "High quality porcelain" , "cup and saucer?" .)

I've seen this clue in The Sunday Times.
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