Blithering ethicist, most irritating (8)

I believe the answer is:

itchiest

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

'blithering ethicist' is the wordplay.
'ethicist' can be anagrammed to 'ITCHIEST'.
But, I'm not clear how this is indicated.

Can you help me to learn more?

(Other definitions for itchiest that I've seen before include "Most restless" , "extremely irritating" .)

I've seen this clue in The Guardian.

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