Crossword Genius

Such cards are no credit to anyone (5)

Ross

I believe the answer is:

debit

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'such cards are' is the definition.
Although both the answer and definition are singular nouns, I can't understand how they can define each other.

I cannot understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for debit that I've seen before include "Record of a sum owed" , "Sum taken from account" , "Payment made or owed" , "Sum removed from a bank account" , "Accounting entry showing sums owing" .)

I've seen this clue in the Evening Standard.
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