What does "sir" mean?

Additional senses

1. 2.An English rendering of the LAtin Dominus, the academical title of a bachelor of arts; -- formerly colloquially, and sometimes contemptuously, applied to the clergy. Nares. Instead of a faithful and painful teacher, they hire a Sir John, which hath better skill in playing at tables, or in keeping of a garden, than in God's word. Latimer.
2. 3.A respectful title, used in addressing a man, without being prefixed to his name; -- used especially in speaking to elders or superiors; sometimes, also, used in the way of emphatic formality. "What's that to you, sir" Sheridan. Note: Anciently, this title, was often used when a person was addressed as a man holding a certain office, or following a certain business. "Sir man of law." "Sir parish priest." Chaucer. Sir reverance. See under Reverence, n.