Howler monkey blowing top? (5)

I believe the answer is:

error

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'howler' is the definition.
(I've seen this before)

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

(Other definitions for error that I've seen before include "Mistake or mishap" , "Miscarriage of justice" , "Faulty judgment" , "Trial and ___" , "wrong" .)

I've seen this clue in The Times and The Sunday Times.

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