| Meaning | Category |
| Of Terrestrial Origin | Miscellaneous->Science Fiction |
| Once- Through Oil | Governmental->Transportation |
| One Time Only | Business->Accounting Business->General |
| One To One | Academic & Science->Mathematics |
| One-Time-Only | Governmental->NASA |
| Operations And Training Officer | Governmental->Military |
| Ordo Templi Orientis | International->Latin |
| Otology | Medical->Physiology |
| Otomian Languages | Regional->Language Codes (3 Letters) |
| Overture To Orchestra | Community->Music |
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