Funny man and straight man, one overshadowed by other at first (4)

I believe the answer is:

fool

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'funny man' is the definition.
The definition and answer can be both people as well as being singular nouns.
Perhaps 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 fool that I've seen before include "Part of 1 25 [KING LEAR]" , "Ass - pudding" , "Nincompoop" , "Deceive" , "Ass; a dessert" .)

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