SI

Si, si, or SI may stand for:

• 'SI', the Système International d'Unités (the 'metric' International System of Units)
• one of two Spanish words pronounced like "see":
  • sí (accented) for "yes" and
  • si (unaccented) for "if"
• a French word pronounced like "see" meaning "yes, on the contrary", "as," "however," "so," and "if."
• in music, Si, the seventh note of solfege
• in chemistry, Si, the chemical symbol for silicon
• in Mohican mythology, Si, the lunar deity
• Sinhalese language, (ISO 639 alpha-2)
• Slovenia (ISO 3166-1 alpha-2 country code, SI)
• in British law, a Statutory Instrument
• Smithsonian Institution
• Socialist International
• Spokane International Railroad (AAR reporting mark SI)
• Sports Illustrated
• Sports Interactive
• Situationist International
• Staten Island, a borough of New York City and an island in the Hudson River
• Swedish Institute (Svenska institutet)
• Supplemental Instruction
• Sexual Intercourse (medical abbreviation, not common usage)
• Self-injury or self-harm
• SI is the acronym for Swarm Intelligence
• In mathematics, si or Si is the Sine integral
• the IATA code for Skynet Airlines
• The Si is a self-replicating artifact in ADOM
• The Si designation is used by Honda to denote high-performance variants of models they manufacture