1. a respectful term of address used to a man.
2. a term of address to a man in a position of authority, as a teacher, army officer, etc.
3. ( cap. ) the distinctive title of a knight or baronet: Sir Joh Bjelke-Petersen.
4. ( cap. ) a title of respect for some notable personage of ancient times: Sir Pandarus of Troy.
5. an ironic or humorous title of respect: sir critic.
6. ( with children ) a male teacher: Sir said I could go.
7. Archaic. a title of respect prefixed to a noun designating profession, rank, etc.: sir priest.
8. Obsolete (a form of address used with scornful or reproachful force): Pull yourself together, sir!
[weak var. of SIRE ]