Supply side finally failing - it’s a joke (4)

I believe the answer is:

quip

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'a joke' is the definition.
(I know that quip is a type of joke)

I don't understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for quip that I've seen before include "Funny remark" , "Bon mot" , "Quick witty remark" , "Off-the-cuff joke" , "Verbal sally" .)

I've seen this clue in The Independent.

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