English abbreviations from o3 to oac
- O3 (Ozone)
- O3O (O3o)
- O4 (Officer grade: Captain or Colonel)
- O5 (Officer grade: Commander or Lieutenant Colonel)
- O6 (Officer grade: Captain or Colonel)
- O7 (Officer grade: Commodore, Rear Admiral (Lower Half), or Brigadier General)
- O8 (Officer grade: Rear Admiral (Upper Half), or Major General)
- O9 (Officer grade: Vice Admiral or Lieutenant General)
- OA (Occupational Analysis)
- OAA (OxAloAcetate)
- OAB (Ordem dos Advogados do Brasil (Brazilian Law Board))
- OAC (Organization for African Community)