Pronunciation: (sûr),[key] —n. 1. a respectful or formal term of address used to a man: No, sir. 2. (cap.) the distinctive title of a knight or baronet: Sir Walter Scott. 3. (cap.) a title of respect for some notable personage of ancient times: Sir Pandarus of Troy. 4. a lord or gentleman: noble sirs and ladies. 5. an ironic or humorous title of respect: sir critic. 6. Archaic.a title of respect used before a noun to designate profession, rank, etc.: sir priest; sir clerk.