Puzzle producing what sounds like a bad-tempered sign of approval (8)

I believe the answer is:

acrostic

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

I can't explain the rest of the clue.

(Other definitions for acrostic that I've seen before include "Verse where certain letters in each line spell out a word or phrase" , "Form of word puzzle" , "Word puzzle using first letters" , "Puzzle involving leading characters" , "Legal document" .)

I've seen this clue in The Guardian.

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