Dictionary.com Unabridged (v 1.1) - Cite This Source - Share This

American Heritage Dictionary - Cite This Source - Share This

sir       (sûr)  Pronunciation Key  n.   Sir Used as an honorific before the given name or the full name of baronets and knights. Used as a form of polite address for a man: Don't forget your hat, sir. Used as a salutation in a letter: Dear Sir or Madam. [Middle English, variant of sire, sire; see sire.]

Online Etymology Dictionary - Cite This Source - Share This
sir 

WordNet - Cite This Source - Share This

sir
noun
1.	term of address for a man
2.	a title used before the name of knight or baronet

Free On-line Dictionary of Computing - Cite This Source - Share This

SIR
1. An early system on the IBM 650.
[Listed in CACM 2(5):16, May 1959].
2. Serial Infrared. An infrared standard from IrDA, part of IrDA Data. SIR supports asynchronous communications at 9600 bps - 115.2 Kbps, at a distance of up to 1 metre.
[Reference?]
(1999-10-14)

Webster's Revised Unabridged Dictionary - Cite This Source - Share This

Sir

Sir\, n. [OE. sire, F. sire, contr. from the nominative L. senior an elder, elderly person, compar. of senex,senis, an aged person; akin to Gr. ??? old, Skr. sana, Goth. sineigs old, sinista eldest, Ir. & Gael. sean old, W. hen. Cf. Seignior, Senate, Seneschal, Senior, Senor, Signor, Sire, Sirrah.]

1. A man of social authority and dignity; a lord; a master; a gentleman; -- in this sense usually spelled sire. [Obs.]

He was crowned lord and sire. --Gower.

In the election of a sir so rare. --Shak.

2. A title prefixed to the Christian name of a knight or a baronet.

Sir Horace Vere, his brother, was the principal in the active part. --Bacon.

3. 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.

4. 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.

American Heritage Abbreviations Dictionary 3rd Edition - Cite This Source - Share This

SIR shuttle imaging radar