/ ˈmɪstə(r); NAmE / noun
1.
Mister the full form, not often used in writing, of the abbreviation Mr
2.
( informal ) used, especially by children, to address a man whose name they do not know :
Please, mister, can we have our ball back?
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WORD ORIGIN
mid 16th cent.: weakened form of master in unstressed use before a name.