Expression tense for Mike and Wally (5)

I believe the answer is:

idiot

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'wally' is the definition.
Both the definition and answer are singular nouns.
Maybe there's an association between them I don't understand?

I don't understand the rest of the clue.

Can you help me to learn more?

(Other definitions for idiot that I've seen before include "'The -----'. novel by Dostoyevsky (1868)" , "Jackass" , "Silly person or dimwit" , "The - (Dostoievsky)" , "Moron, fool" .)

I've seen this clue in The Independent.

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