Excessive irregular deductions ruined super (5)

I believe the answer is:

undue

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'excessive' is the definition.
(I know that excessive can be written as undue)

I cannot understand how the rest of the clue works.

Can you help me to learn more?

(Other definitions for undue that I've seen before include "Not warranted" , "Unwarranted, inordinate" , "More than appropriate" , "Inappropriate - excessive" , "Excessive, disproportionate" .)

I've seen this clue in the Sydney Morning Herald.

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