Definition of sir

• n. - A man of social authority and dignity; a lord; a master; a gentleman; -- in this sense usually spelled sire.
• n. - A title prefixed to the Christian name of a knight or a baronet.
• n. - An English rendering of the LAtin Dominus, the academical title of a bachelor of arts; -- formerly colloquially, and sometimes contemptuously, applied to the clergy.
• n. - 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.