A short cut in decimal rates (3,4)

I believe the answer is:

per cent

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'cut in decimal rates' is the definition.
Although both the answer and definition are singular nouns, I can't see how one could define the other.

'a short' is the wordplay.
'a' becomes 'per'.
'short' becomes 'cent' (I am not sure about this - if you are sure you should believe this answer much more).
'per'+'cent'='PER CENT'

Can you help me to learn more?

(Another definition for per cent that I've seen is " Proportion".)

I've seen this clue in The Globe and Mail.

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