| S.No. | Short Form | Full Form | Category | Country | Popularity |
| 1 |
SI |
Système International d‘unités French [International System of Units] |
Academic & Science > Units |
Worldwide |
|
| 2 |
SI |
Statutory Instrument |
Governmental > Rules & Regulations |
United Kingdom |
|
| 3 |
SI |
Sub-Inspector |
Governmental > Police |
India |
|
| 4 |
SI |
Sports Illustrated |
News & Entertainment > Journals & Publications |
United States |
|
| 5 |
SI |
Samahang Ilokano |
Associations & Organizations > Regional Organizations |
Philippines |
|
| 6 |
SI |
Societas Iesu Latin [Society of Jesus] |
Society & Culture > Religion & Spirituality |
Worldwide |
|
| 7 |
SI |
Sports Interactive |
Business > Companies & Corporations |
United Kingdom |
|
| 8 |
SI |
Skynet Airlines |
Transport & Travel > Airline Codes |
Ireland |
|
| 9 |
SI |
Spokane International Railroad |
Transport & Travel > Rail Transport |
United States |
|
| 10 |
SI |
St. Ignatius College Preparatory |
Academic & Science > Universities & Institutions |
United States |
|
| 11 |
SI |
Silay Institute |
Academic & Science > Universities & Institutions |
Philippines |
|
| 12 |
SI |
Smithsonian Institution |
Regional > Buildings & Landmarks |
United States |
|
| 13 |
SI |
Survey of India |
Governmental > Departments & Agencies |
India |
|
| 14 |
SI |
Svenska Institutet Swedish [Swedish Institute] |
Governmental > Departments & Agencies |
Sweden |
|
| 15 |
SI |
Schweizer Informatik Gesellschaft German [Swiss Informatics Society] |
Associations & Organizations > Professional Associations |
Switzerland |
|
| 16 |
SI |
Solidaritat Catalana per la Independència Catalan [Catalan Solidarity for Independence] |
Governmental > Politics |
Spain |
|
| 17 |
SI |
Socialist International |
Governmental > Politics |
Worldwide |
|
| 18 |
SI |
Solidaridad e Igualdad Spanish [Solidarity and Equality] |
Governmental > Politics |
Argentina |
|
| 19 |
SI |
Survival International |
Associations & Organizations > Medical Organizations |
United Kingdom |
|
| 20 |
SI |
Province of Siena |
Transport & Travel > License Plates |
Italy |
|
| 21 |
SI |
Slovenia |
Regional > Countries |
Slovenia |
|
| 22 |
si |
Slovenia (TLD) |
Computing > Domain Names (TLD) |
Slovenia |
|
| 23 |
Si |
Silicon |
Academic & Science > Chemistry |
Worldwide |
|
| 24 |
SI |
Signal Integrity |
Academic & Science > Electronics |
Worldwide |
|
| 25 |
SI |
Sacroiliac |
Medical > Anatomy & Physiology |
Worldwide |
|
| 26 |
SI |
Small Intestine |
Medical > Anatomy & Physiology |
Worldwide |
|
| 27 |
SI |
Substantia Innominata |
Medical > Anatomy & Physiology |
Worldwide |
|
| 28 |
SI |
Suicidal Ideation |
Medical > Diseases & Conditions |
Worldwide |
|
| 29 |
SI |
Shift In |
Computing > General Computing |
Worldwide |
|
| 30 |
SI |
Swarm Intelligence |
Computing > Programming & Development |
Worldwide |
|
| 31 |
SI |
System Integrator |
Computing > General Computing |
Worldwide |
|
| 32 |
SI |
Spark-Ignition |
Technology > Automotive |
Worldwide |
|
| 33 |
SI |
Station Inspector |
Governmental > Police |
Singapore |
|
| 34 |
SI |
Simple Interest |
Business > Finance |
Worldwide |
|
| 35 |
si |
Sinhalese |
Regional > Language Codes |
Sri Lanka |
|
| 36 |
SI |
Stroke Index |
Sports & Recreations > Other Games |
Worldwide |
|
| 37 |
SI |
Supplemental Instruction |
Academic & Science > Universities & Institutions |
Worldwide |
|