Other
- Cibao International Airport, IATA airport code
- Sail Training International, an international maritime education charity
- Science-Technics-Industry, an epistemological concept in editology
- Sexually transmitted infection, see sexually transmitted disease
- Soft tissue injury
- Sony, Toshiba, IBM—co-developers of the Cell microprocessor
- South Thailand insurgency
- STI International, firearms manufacturer
- Subaru Impreza WRX STI, high performance cars
- Subaru Tecnica International, Subarus motorsports division
- SunTrust Banks, a bank holding company whose NYSE stock symbol is STI
- Verkehrsbetriebe STI, a public transport operator in the canton of Bern, Switzerland
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