S1
| Acronym | Definition |
|---|---|
| S1 | Secondary 1 (schools; Hong Kong) |
| S1 | Supplement 1 (to a document or publication) |
| S1 | Starboard 1 (US NASA) |
| S1 | Adjutant (Army) |
| S1 | Personnel Office (USMC) |
| S1 | First Heart Sound |
| S1 | Subfragment 1 (biophysics) |
| S1 | Sleep Mode 1 (high-energy computer power-down state) |