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Whomsoever
Rare Usage
The word 'whomsoever' is rarely used in everyday conversation but may appear in formal writing. 
Emphasis on Any
'Whomsoever' is used when emphasizing that anyone at all could be chosen or affected. 
Impersonal Constructs
It's often found in expressions that need to be impersonal, like 'To whomsoever it may concern'. 