Allow Harold to be deadly (6)

I believe the answer is:

lethal

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'be deadly' is the definition.
(synonyms)

'allow harold' is the wordplay.
'allow' becomes 'let' (synonyms).
'harold' becomes 'hal' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'let'+'hal'='LETHAL'

'to' acts as a link.

Can you help me to learn more?

(Other definitions for lethal that I've seen before include "Death-dealing" , "Able to cause death" , "describing a killer?" , "All the change can be deadly." , "Terminal" .)

I've seen this clue in The Mirror.

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