A gentleman.
A person (chiefly male) of strength, integrity, and honor or compassion.
A man of a higher rank or position.
to a teacher.
to a knight or other low member of the peerage.
to a superior military officer.
A respectful term of address to a man of higher rank or position
A respectful term of address to an adult male (often older), especially if his name or proper title is unknown.
To address (someone) using "sir".