Si

Si or 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"
• in music, Si, the seventh note of solfege
• in chemistry, Si, a symbol for the chemical element of silicon
• in Mohican mythology, Si, the lunar deity
• Sinhalese language, (ISO 639 alpha-2)
• Slovenia (ISO 3166-1 alpha-2 country code, SI)
• in UK law, a statutory instrument
• Smithsonian Institution
• Socialist International
• 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