What could be finer than a riddle? (5)

I believe the answer is:

sieve

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'a riddle?' is the definition.
(riddle is a kind of sieve)

I can't explain the rest of the clue.

(Other definitions for sieve that I've seen before include "Kitchen strainer" , "Eratosthenes' invention" , "used by the Jumblies" , "Mesh used for straining or sifting" , "Forgetful head is like it" .)

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

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