| 1. | a respectful or formal term of address used to a man: No, sir. |
| 2. | (initial capital letter ) the distinctive title of a knight or baronet: Sir Walter Scott. |
| 3. | (initial capital letter ) 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. |
| SIR shuttle imaging radar |