Allowed American Henry to be murderous (6)

I believe the answer is:

lethal

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'be murderous' is the definition.
(I've seen this in another clue)

'allowed american henry' is the wordplay.
'allowed' becomes 'let' (to let is to allow or permit).
'american henry' becomes 'hal' (short for Henry. I am not sure about the 'american' bit.).
'let'+'hal'='LETHAL'

'to' is the link.

Can you help me to learn more?

(Other definitions for lethal that I've seen before include "Destructive" , "Terminal" , "Murderous" , "Deadly dangerous" , "bringing about the end?" .)

I've seen this clue in The Sun.

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