Dull fool annoyed (7)

I believe the answer is:

anodyne

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

'fool annoyed' is the wordplay.
'annoyed' anagrams to 'ANODYNE'.
Though, I'm not sure how the anagram is indicated.

Can you help me to learn more?

(Other definitions for anodyne that I've seen before include "Relieving hurt" , "Easing pain and distress - annoyed (anag)" , "not causing disagreement" , "Unlikely to offend" , "A drug that relieves pain" .)

I've seen this clue in the Sydney Morning Herald.

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