Crossword Genius

One's idiotic hum? (7)

Ross

I believe the answer is:

halfwit

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

This clue could be a double definition.

'one's' is the first definition.
Although both the answer and definition are singular nouns, I cannot understand how one could define the other.

'idiotic hum?' is the second definition.
Although both the answer and definition are singular nouns, I cannot see how one could define the other.

Can you help me to learn more?

(Other definitions for halfwit that I've seen before include "dunce?" , "One only 50% all there?" , "Being stupid" , "Charlie?" , "Idiot" .)

I've seen this clue in The Guardian.
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