| opisthorchiasis | Opisthorchiasis |
| opisthotonos | Opisthotonus |
| Opisthotonus | Opisthotonus |
| Opistognathidae | Brunnenbauer |
| opium | Opium |
| opium addict | Opiumsüchtige |
| opium addiction | Opiumsucht |
| opium alkaloid | Mohn-Alkaloid |
| opium consumption | Opiumkonsum |
| opium den | Opiumhöhle |
| opium growing | Opiumanbau |
| opium pipe | Opiumpfeife |
| opium plantation | Opiumanbau |
| opium plantations | Opiumanbau |
| opium poppy | Schlafmohn |
| opium poppy field | Schlafmohnfeld |
| opium smoker | Opiumraucher |
| opium smuggling | Opiumschmuggel |
| opium tea | Opiumtee |
| opium tincture | Opiumtinktur |
| opium trade | Opiumgeschäft |
| opium traffic | Opiumhandel |
| Opium War | Opiumkrieg |
| Opium Wars | Opiumkriege |
| Oplegnathidae | Schnabelbarsche |
| Oplontis | Oplontis |
| OPML | Outline Processor Markup Language |
| Opoczno | Opoczno |
| Opoczno County | Powiat Opoczyński |
| Opole | Oppeln |
| Opole County | Powiat Opolski |
| Opole Lubelskie County | Powiat Opolski |
| Opole Voivodeship | Woiwodschaft Oppeln |
| opor-garai | Urlaub |
| Oporto | Portwein |
| opossum | Beutelratte |
| opossum rat | Affenschwanz-Ratte |
| opossums | Beutelratten |
| opp. : opposite | gegenüber, entgegengesetzt |
| Oppach | Oppach |
| Oppavia | Oppavia |
| Oppdal | Oppdal |
| Oppel-Kundt illusion | Oppel-Kundt-Täuschung |
| Oppenau | Oppenau |
| Oppenauer oxidation | Oppenauer-Oxidation |
| Oppenheim | Oppenheim |
| Oppenheim am Rhein | Oppenheim am Rhein |
| Oppens | Oppens VD |
| Oppenweiler | Oppenweiler |
| Oppershausen | Oppershausen |
| Oppidum | Oppidum |
| Oppidum of Manching | Oppidum von Manching |
| Oppland | Oppland |
| Oppligen | Oppligen |
| Opponens digiti minimi muscle | Musculus opponens digiti minimi |
| Opponens pollicis muscle | Musculus opponens pollicis |
| opponent | entgegengesetzt |
| opponent color | Gegenfarbe |
| opponent in the final | Finalgegner |
| opponent of Hitler | Gegner Hitlers |
| opponent of nuclear power | Atomgegner |
| opponent of nuclear weapons | Kernwaffengegner |
| opponent of slavery | Sklavereigegner |
| opponent of war | Kriegsgegner |
| opponent process | Gegenfarbtheorie |
| opponents | Gegenspieler |
| opponents in the final | Finalgegner |
| opponents of nuclear power | Atomkraftgegner |
| Opponitz | Opponitz |
| opportune | passend |
