Randomly block a number after king outlawed weapon (7,4)

I believe the answer is:

nuclear bomb

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'randomly block a number after king' is the definition.
I don't know anything about this answer so I can't judge whether this works.

'outlawed weapon' is the wordplay.
'outlawed' becomes 'nuclear' (I am not sure about this - if you are sure you should believe this answer much more).
'weapon' becomes 'bomb' (I have seen 'Explosive weapon ' mean 'bomb' so perhaps 'weapon' could also mean 'bomb').
'nuclear'+'bomb'='NUCLEAR BOMB'

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I've seen this clue in the Sydney Morning Herald.

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