| OMSA | Office of Medical Student Affairs 
| Others |
| OMSA | Office of Minority Student Affairs
| Others |
| OMSA | Office of Multicultural Student Affairs
| Others |
| OMSA | Offshore Marine Service Association
| Others |
| OMSA | Offshore Marine Services Alliance
| Others |
| OMSA | Oficina Metropolitana de Servicios de Autobuses
| Others |
| OMSA | Ogden Museum of Southern Art
| Others |
| OMSA | Okotoks Minor Soccer Association
| Others |
| OMSA | Old Mans Soccer Association
| Others |
| OMSA | Online Media Standards Authority
| Others |
| OMSA | Ontario Medical Secretaries Association
| Others |
| OMSA | Ontario Medical Students Association
| Others |
| OMSA | Open Manage Server Administrator
| Others |
| OMSA | Opticalman Seaman Apprentice
| Others |
| OMSA | Oral and Maxillofacial Surgery Assistants
| Others |
| OMSA | Orders and Medals Society of America
| Others |
| OMSA | Organisation et Management des Services Automobile
| Others |
| OMSA | Otago Malaysian Students Association
| Others |
| OMSA | Otago Malaysian Students' Association
| Others |