Mister

n. 先生

Mis.ter

n.Abbr. Mr.（名词）缩写 Mr.
Used as a courtesy title before the surname, full name, or professional title of a man, usually written in its abbreviated form:
先生：一个男子的姓，全名或职务前的礼貌称谓，通常用作略写形式：
例句：
Mr. Jones; Mr. Secretary.
琼斯先生；秘书先生

Used as the official term of address for certain U.S. military personnel, such as warrant officers.
长官：某美国军事人员的官方称呼，如海军二级准尉们
mister Informal Used as a form of address for a man:
mister 【非正式用语】 先生：用作对男士称呼的形式：
例句：
Watch your step, mister.
先生，脚下留神

Informal Used as a term of reference by a woman of her husband.
【非正式用语】 先生：妇女提及其丈夫时的称呼

来源：
Alteration of master
master的变化