SI
- si — (s) Sinhalese language (ISO 639-1 code)
- Si — (s) Silicon
- SI
- (s) Slovenia (ISO 3166 and FIPS 10-4 country code digram)
- (i) Socialist International
- Sports Illustrated
- Système International (French, International System of Units)
- SIA — (s) Singapore Airlines (ICAO code)
- SIA — (i) Survivors of Incest Anonymous
- SIAM — (i) Society for Industrial and Applied Mathematics
- SIC — (a) Standard Industrial Classification
- SICS — (a/i) Swedish Institute of Computer Science
- SIDS — (a) Sudden Instant Death Syndrome
- SIDU — (i) select, insert, delete, update. See Create, read, update and delete
- SIF — (i) Selective Identification Feature
- SIFF — (i) Successor IFF
- SIG
- (i) Schweizerische Industrie Gesellschaft (German, "Swiss Industry Company"). See also SIG Sauer, a firearms manufacturer spun off from the aforementioned company in 2000.
- (p) .signature (UNIX shell/Internet standard file name)
- (a/i) Special Interest Group
- SIGCAT — (a) Special Interest Group for CD-ROM Applications and Technology
- SIGINT — (p) Signals Intelligence
- SIGMET — (p) Significant Meteorological Information
- SIIT
- (i) Saskatchewan Indian Institute of Technologies (Canadian university)
- Sirindhorn International Institute of Technology (Thai university)
- Stateless IP/ICMP Translation algorithm
- SIMAC — (a) Semantic Interaction with Music Audio Contents
- SIMLAS — (p) Soldier Integrated Multipurpose Laser System
- SIMM — (a) Single In-line Memory Module
- SIMNET — (p) SIMulator NETwork, later SIMulation NETwork
- SIMNET-D - (p) SIMNET-Developmental
- SIMP — (a) Strongly Interacting Massive Particle
- SIMPLE
- (a) Satellite Interactive Multimedia Platform for Low-cost Earth stations
- (p) Savings Incentive Match Plan for Employees (as used in SIMPLE IRA)
- (a) Standard Interface for Multiple Platform Link Evaluation (NATO STANAG 5602)
- sin — (s) Sinhalese language (ISO 639-2 code)
- SIN — (a) Social Insurance Number (Canada)
- SINCGARS — (p) SINgle Channel Ground and Airborne Radio System
- SIP
- (i) Session Initiation Protocol
- State Implementation Plan
- System Improvement Program
- Systematic Investment Plan
- SIPP — (a) Self-Invested Personal Pension
- Siri – (a) Speech Interpretation and Recognition Interface (Apple iOS software)
- SIRI – (a) Service Interface for Real Time Information
- SiS — (i) Silicon Integrated Systems
- SIS — (i) UK Secret Intelligence Service (also known as MI6)
- SISO
- (a) Simulation Interoperability Standards Organization
- Society of Independent Show Organizers
- SIW — (i) Simulation Interoperability Workshop
- SIYSS — (i) Stockholm International Youth Science Seminar
Read more about this topic: List Of Acronyms And Initialisms: S