| Acronym | Definition |
|---|
| NSI | No Smoking Indoors |
| NSI | Network Solutions, Inc. |
| NSI | National Security Information |
| NSI | North-South Institute (Canadian Economic Think Tank) |
| NSI | National System of Innovation (various nations) |
| NSI | NASA Science Internet |
| NSi | Nova Slovenija (New Slovenia) |
| NSI | National Security Intelligence (fictional) |
| NSI | National Security Institute |
| NSI | Nielsen Station Index |
| NSI | Nutrition Screening Initiative |
| NSI | Nuclear Surety Inspection |
| NSI | National Statistical Institutes |
| NSI | Needle Stick Injury |
| NSI | National Savings and Investments (UK) |
| NSI | National Student Index (New Zealand) |
| NSI | Nomura Securities International |
| NSI | Naval Science Instructor |
| NSI | NASA Standard Initiator |
| NSI | National Satellite Initiative (Canada) |
| NSI | National Space Institute |
| NSI | Network Side Interface (DOCSIS) |
| NSI | Network Service Interface |
| NSI | Neurological Society of India |
| NSI | Not Signed In |
| NSI | Yaounde, Cameroon - Nsimalen (Airport Code) |
| NSI | National Shipbuilding Initiative |
| NSI | Net Satisfaction Index |
| NSI | Next Sequential Instruction |
| NSI | Non-Standard Neutrino Interactions |
| NSI | Nuclear Safety Institute (est. 1990; Russia) |
| NSI | Neurosurgery Institute (Russian Federation) |
| NSI | Nonstandard Item |
| NSI | Not Sufficient Information |
| NSI | Nordisk Systemintegrering AB (Stockholm, Sweden) |
| NSI | National Science Institute |
| NSI | Nuclear Safety Inspection |
| NSI | Name Server Interface |
| NSI | New South Interactive |
| NSI | Nonstocked Item |
| NSI | Negotiation Systems International |
| NSI | Non-Serious Injury |
| NSI | Name Space Interface (Bellcore) |
| NSI | Newsprint South, Inc. |
| NSI | Non Service Independent |
| NSI | No Suicidal Ideations (medicine) |
| NSI | New Suspense Item |
| NSI | Net Sales Income (finance) |
| NSI | Northern Saline, Inc. |
| NSI | Numeric System Identifier |
| NSI | Negative Social Imprinting (psychology) |
| NSI | Naviguer Sur Internet (French: Surfing the Internet) |
| NSI | Non-Standard Inference |
| NSI | Negative Social Impact (HIV/AIDS) |
| NSI | Nutrition Santé International (French: Nutrition Health International) |
| NSI | Nuovi Stati Indipendenti (Italian: New Independent States) |
| NSI | Negative Self Image (psychology) |
| NSI | Network Software Inspector (Secunia) |
| NSI | National Standards Institute |
| NSI | Never Stop Improving |