Here is the meaning of the word, SIR

Sir ( n. ) - A man of social authority and dignity; a lord; a master; a gentleman; -- in this sense usually spelled sire.
Sir ( 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.
Sir ( n. ) - A title prefixed to the Christian name of a knight or a baronet.
Sir ( 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.