sir

noun

1. a man of rank; lord
2. a respectful term of address used to a man: not followed by the given name or surname and often used in the salutation of a letter: Dear Sir
3. the title used before the given name or full name of a knight or baronet: Sir Walter Ralegh
4. Archaic a term of address used with the title of a man's office, rank, or profession: sir priest, sir judge, sir knight