Tom's asinine behaviour? (7)

I believe the answer is:

foolery

I'm a little stuck... Click here to teach me more about this clue!

This might be a double definition.

'tom's' is the first definition.
Although both the answer and definition are singular nouns, I cannot understand how they can define each other.

'asinine behaviour?' is the second definition.
The answer and definition can be both acts as well as being singular nouns.
Maybe you can see an association between them that I can't see?

Can you help me to learn more?

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