| Meaning | Category |
| Oceanic Automation Program | Governmental->Transportation |
| Old Age Pension | Business->Positions |
| Old Age Pensioner | Governmental->Military |
| Old Age Pensioners | Governmental->Military |
| Old Age Person | Community->Law |
| Old Age Premium | Business->Positions |
| Oldtimers Against Progress | Miscellaneous->Funnies |
| On-line Action Plan | Business->General |
| One Act Play | Community->Performing Arts |
| Online Artist's Project | Internet |
| Online Artists Project | Community |
| Osaka Amenity Park | Community |
| Osteoarthropathy | Medical->Physiology |
| Outdoor Adventure Program | Community |
| Outgoing Active And Positive | Community->Educational |
| Outstanding Award Program | Community->Educational |
| Overseas Academic Program | Academic & Science->Universities |
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