| Acronym | Definition |
|---|
| SUN | Sunday |
| SUN | Sunoco |
| SUN | Sunriver (Amtrak station code; Sunriver, OR) |
| SUN | Scaling Up Nutrition |
| SUN | Soul of the Ultimate Nation (role-playing game) |
| SUN | Second University of Naples (Italy) |
| SUN | Stanford University Network |
| SUN | Sistema de Ubicación y Nivelación (Spanish: Location and Grading System; Guatemala) |
| SUN | Seconda Università Degli Studi di Napoli (Italian: Second University of Naples; est. 1991) |
| SUN | Saskatchewan Union of Nurses (Canada) |
| SUN | Service User Network (mental health) |
| SUN | Southern Utah News (Kanab, UT) |
| SUN | Seattle Urban Nature (Washington) |
| SUN | Services U Need (various locations) |
| SUN | Surat Utang Negara (Indonesian: sovereign bond) |
| SUN | Sun Valley/Hailey, ID, USA (Airport Code) |
| SUN | Senior Unlimited Nudes (San Francisco, CA) |
| SUN | Sunset Railway Company |
| SUN | Students United for Nature |
| SUN | Seniors United Nutrition (Volusia County, Florida) |
| SUN | Shipping Unit Number (shipping) |
| SUN | Searching for Unregistered Names |