| ovvietà | evidence |
| ovvio | clear |
| OWA | Owa |
| Owain ap Tomas ap Rhodri | Owain Lawgoch |
| Owain Glyndŵr | Owain Glyndŵr |
| Owain Goch ap Gruffydd | Owain Goch ap Gruffydd |
| Owain Gwynedd | Owain Gwynedd |
| Owain mab Urien | Owain mab Urien |
| Owari | Owari Province |
| Owen Willans Richardson | Owen Willans Richardson |
| Owen Wilson | Owen Wilson |
| Owensboro | Owensboro |
| Owhyee | Owhyee |
| Owingen | Owingen |
| OWL | Owl |
| Owner Free Filing System | Owner free filing system |
| Owrócz | Ovruch |
| Oxalidaceae | Oxalidaceae |
| Oxalis corniculata | Oxalis corniculata |
| Oxalis pes-caprae | Oxalis pes-caprae |
| Oxalis stricta | Oxalis stricta |
| Oxazine | Oxazines |
| Oxfam | Oxfam |
| Oxford | Oxford |
| Oxford English Dictionary | Oxford English Dictionary |
| Oxford Street | Oxford Street |
| Oxfordshire | Oxfordshire |
| Oxprenololo | Oxprenolol |
| Oxygene | Oxygen |
| OY | Oy |
| Oy-Mittelberg | Oy-Mittelberg |
| Oymapınar | Oymapinar Dam |
| Oyo | Oyo State |
| Oyá | Oya |
| Oyón | Oyón-Oion |
| OZ | Ounce |
| Oza dos Ríos | Oza dos Ríos |
| Ozamiz | Ozamiz City |
| ozelot | ocelot |
| oziare | loaf |
