Look up SIR, sir, Sir in Wiktionary, the free dictionary.

SIR or Sir may refer to:

• Sir, a respectful title for a man
• Sir (A Series of Unfortunate Events), a Guardian character in A Series of Unfortunate Events
• Sampling Importance Resampling
• Sigma Iota Rho
• Signal-to-Interference Ratio
• Singapore Infantry Regiment
• Staten Island Railway
• Statutory Invention Registration
• Surrey Iron Railway
• Sirene, a type of white brine cheese made in Bulgaria and Republic of Macedonia
• The SIR model, one of the compartmental models in epidemiology
• Serial Infrared, a category of Infrared Data Association
• Secondary Image Registration, a type of passive autofocus
• Supplemental Inflatable Restraint or airbag
• Saskatchewan International Raceway, a Saskatoon drag strip
• Société Ivoirienne de Raffinage (Ivoirian Refining Company), Côte d'Ivoire state/private petroleum partnership

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