Honest leaders sound dull (5)

I believe the answer is:

hohum

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'dull' is the definition.
I don't know anything about this answer so I can't tell whether it can be defined by this definition.

'honest leaders sound' is the wordplay.
'honest leaders' becomes 'ho' (I can't justify this - if you can you should give a lot more credence to this answer).
'sound' becomes 'hum' (humming is a kind of sounding).
'ho'+'hum'='HOHUM'

Can you help me to learn more?

I've seen this clue in The Daily Express.

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