a title (written Esq.) used in the address of a letter after a man's family name (instead of Mr before it)

Mr.

(always written Mr) (used in front of the name of a man who has no other title) 'Mr Green'; (used by children to a man) 'Please, mister, can I have my ball back?'

Mr

used by children to a male teacher, by a shop assistant to a man etc; used to begin a formal letter to a man

mister