Mr

Mr BrE AmE British English, Mr. American English /ˈmɪstə $ -ər/
1. used before a man’s family name to be polite when you are speaking to him, writing to him, or talking about him:
Mr Smith is the headteacher.
Mr. John Smith
Mr and Mrs Smith
2. used when speaking to a man in an official position:
Mr Chairman
Mr. President ⇨ ↑madam(3)
3. Mr Right a man who would be the perfect husband for a particular woman:
She’s finally found Mr. Right.
4. Mr Big informal the leader or most important person in a group, especially a criminal group
5. Mr Clean informal someone who is honest and always obeys the law
6. Mr Sarcasm/Mr Messy/Mr Forgetful etc spoken used humorously to say that someone has a particular quality or behaves in a particular way:
I don’t think we need any comments from Mr Sarcasm here.
⇨ no more Mr Nice Guy! at ↑guy(5)

Mr.

Mr BrE AmE British English, Mr. American English /ˈmɪstə $ -ər/
1. used before a man’s family name to be polite when you are speaking to him, writing to him, or talking about him:
Mr Smith is the headteacher.
Mr. John Smith
Mr and Mrs Smith
2. used when speaking to a man in an official position:
Mr Chairman
Mr. President ⇨ ↑madam(3)
3. Mr Right a man who would be the perfect husband for a particular woman:
She’s finally found Mr. Right.
4. Mr Big informal the leader or most important person in a group, especially a criminal group
5. Mr Clean informal someone who is honest and always obeys the law
6. Mr Sarcasm/Mr Messy/Mr Forgetful etc spoken used humorously to say that someone has a particular quality or behaves in a particular way:
I don’t think we need any comments from Mr Sarcasm here.
⇨ no more Mr Nice Guy! at ↑guy(5)

Oxford Advanced Learner's Dictionary

Mr

Mr [Mr Messrs] (BrE) (also Mr. NAmE, BrE) [ˈmɪstə(r)] [ˈmɪstər] abbreviation
1. a title that comes before a man's family name, or before his first and family names together
• Mr Brown
• Mr John Brown

• Mr and Mrs Brown

2. a title used to address a man in some official positions
• Thank you, Mr Chairman.
• Mr. President
see also mister
Idioms: Mr Nice Guy ▪ Mr Right
Word Origin:

late Middle English: originally an abbreviation of master; compare with mister.

Cambridge Advanced Learner's Dictionary

Cambridge Advanced Learner's Dictionary - 4th Edition

Mr / ˈmɪs.tə r / / -tɚ / noun

A1 a title used before the family name or full name of a man who has no other title, or when talking to man who holds a particular official position:

Mr Jones/Mr David Jones

[ as form of address ] Good afternoon, Mr Dawson.

We're looking for a Mr (= a man called) George Smith.

It's an honour to have you here today, Mr President.

→ Compare Miss , Mrs , Ms

used when expressing the idea that a man is typical of or represents a quality, activity, or place:

She's still hoping to meet Mr Right (= the perfect man) .

He thinks he's Mr Big (= someone very important) .

Collins COBUILD Advanced Learner’s English Dictionary

Mr

/mɪstə(r)/

Note: in AM, use 'Mr.'

1.
Mr is used before a man’s name when you are speaking or referring to him.
...Mr Grant.
...Mr Bob Price.
...Mr and Mrs Daniels.
N-TITLE

2.
Mr is sometimes used in front of words such as ‘President’ and ‘Chairman’ to address the man who holds the position mentioned.
Mr. President, you’re aware of the system.
N-VOC: N n

Merriam-Webster's Advanced Learner's Dictionary

Merriam-Webster's Advanced Learner's Dictionary:

Mr.

Mr. US or Brit Mr /ˈmɪstɚ/ noun
1 a
- used as a title before the name of a man
• Mr. Doe
• How are you, Mr. Jones?
• Mr. John Doe
- compare mister; see also messrs.
b
- used as a title when speaking to a man who has an honored position or office
• “It's an honor to meet you, Mr. President/Chairman.”
2 a
- used as part of a title for a man who has won a contest
• Mr. Universe
b
- used to refer to a man who is very successful and famous for a particular activity (such as a sport) or who has a particular quality
• He came to be known as Mr. Baseball.
• She thinks her boyfriend is Mr. Wonderful. [=she thinks her boyfriend is wonderful]