(initial capital letter) a conventional title of respect for a man, prefixed to the name and to certain official designations (usually written as the abbreviationMr.).
2.
Informal. sir (used in direct address and not followed by the name of the man addressed): Mister, is this your umbrella?
3.
(initial capital letter) a title prefixed to a mock surname that is used to represent possession of a particular attribute, identity, etc.: Mister Know-it-all.
4.
the informal or social title used in addressing a military warrant officer or any naval officer below the rank of commander.
5.
(especially in military schools and colleges)
a.
a term of respect used by cadets in addressing upperclassmen: used with surname.
b.
a term of disparagement used by upperclassmen in addressing cadets: Mister, tuck in that shirttail!