Untrustworthy partner abused trade rule (9)

I believe the answer is:

adulterer

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'untrustworthy partner' is the definition.
The definition and answer can be both people as well as being singular nouns.
Perhaps they are linked in a way I don't understand?

'abused trade rule' is the wordplay.
'abused' indicates an anagram.
'trade'+'rule'='traderule'
'traderule' anagrammed gives 'ADULTERER'.

Can you help me to learn more?

(Other definitions for adulterer that I've seen before include "Man United playing away" , "Durer tale (anag)" , "Sinner" , "Perhaps playboy" , "Man who cheats on his wife" .)

I've seen this clue in The Independent.

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