Re: You have a word for it?

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Formal would use last name.  If a child calls me "Mr. Nik", it's a
form
of affectionate respect.  At least around here, it tends to be common
with adults or older children in a position of some authority, for
example, a baby sitter.  But, for example, a teacher would be
Mr./Miss/Mrs. + last name.
>>
Reminds me of how young children are taught to refer to family
friends (who are not relatives) as Uncle or Aunt(ie)...

Imperative