| Original proof of Gödel's completeness theorem | Orca | Organic electronics |
| Orson Welles | Oregon | Orbital |
| Organic compoundAn organic compound is any of a large class of chemical compounds whose molecules contain carbon, with exception of carbides, carbonates and carbon oxides. Organic compounds are studied in organic chemistry; many of them, such as proteins, fats, and carbo | Organic chemistryOrganic chemistry is the scientific study of the structure, properties, composition, reactions, and synthesis of organic compounds. Organic nomenclature Organic nomenclature is the system established for naming and grouping organic compounds. Aliphatic co | OrthographyThe orthography of a language is the set of rules of how to write correctly in the language. The term is derived from Greek omicron;ρθ&omicron ortho ("correct") and gamma;ραφο&sigmaf graphos ("that writes") and, in today's |
| OrdovicianThe Ordovician period is the second of the six (seven in North America) periods of the Paleozoic era. The Ordovician follows the Cambrian period and is followed by the Silurian period. The Ordovician named after the Welsh tribe of the Ordovices was define | OreganoOregano Origanum vulgare is a spicy, Mediterranean, perennial herb, particularly common in Greek and Italian cuisines. It is the leaves that are used in cooking, and the dried herb is often more flavourful than the fresh. Classification Oregano (also call | OregonianAn Oregonian is a resident or native of the state of Oregon; The Oregonian is the daily newspaper in Portland. Oregon. |
| Orkhon scriptTurkic people living in Central Asia developed various alphabets in early ages. The earliest known alphabet is the Kokturk Kok Turki Gokturk alphabet developed by Kokturks, a Turkic tribespeople that had established a broad Central Asian empire and reache | Orkhon inscriptionsOrhon (or Orkhon) inscriptions are the oldest known Turkic writings, which were erected near the Orhon River between 732 and 735 in honour of two Kokturk princes named Kul and Bilge. They have been carved on two monuments by old Turkic runes (see Orkhon s | OrrorinOrrorin tugenensis is an extinct species of hominid that is closely related to humans. The name was given by the discoverers who found Orrorin fossils near the village of Tugen, Kenya, and dated them to approximately 6 million years ago. The fossils found |
| Ordered pair | Ordinal number | Organ |
| Organometallic compound | Organelle | Orson Scott Card |
| Order automorphism | Orange | Ordered field |
| Oracle machine | Orangutan | Orbital resonance |
| Organic nomenclature | Orion | Orsini family |
| Orhan I | Orbit | Orthodox Judaism |
| Orienteering | Organometallic chemistry | Orient House |
| Oracle | Oracle Corporation | Organization |
| Ore | Orlando Letelier | Organism |
| Oral contraceptive | Organized crime | Orkney Islands |
| Orders of magnitude | Orimulsion | Organization of the Communist Party of the USSR |
| Oromo | Oral history | Orthogonal frequency division modulation |
| Origin of life | Oriental Orthodoxy | Origen |
| Orchestra | Origin | Orchidaceae |
| Original sin | Order of the Eastern Star | Orthodox Bahá'í Faith |
| Original Amiga chipset | Organization of American States | Organization for Security and Co-operation in Europe |
| Ordinary English | Orange Alternative | Orgy of the Dead |
| Organizers of the September 11, 2001 attacks | Organisation for the Prohibition of Chemical Weapons | Orientalism |
| Orlando Bloom | Orbital revolution | Orientalium Ecclesiarum |
| Ornithology | Orc | Organ donation |
| Orem, Utah | Orange County | Orange County, California |
| Orpheus in the Underworld | Orchestration | Organization of the Islamic Conference |
| Orleans (disambiguation) | Organisation of African Unity | Oregon Trail |
| Organ Pipes National Park | Orange County, Texas | Original Dixieland Jass Band |
| Origami | Orange juice | Order |
| Orogeny | Ortler, Oetzthal and Stubai Ranges | Oresund |
| Orleans County, New York | Orange County, New York | Oral glucose tolerance test |
| Ordeal in Space | Orange Book | Orrery |
| Ortolan Bunting | Oral law | Order (biology) |
| Organisation de l'Armée Secrète | Oravita | Oradour-sur-Glane |
| Oromë | Organic acid | Organic |
| Ornament (music) | Orator | Original equipment manufacturer |
| Oresund Bridge | Orthoptera | Orange (colour) |
| Orange (fruit) | Orange (company) | Organic farming |
| Orlando Magic | Order of the Garter | Orange County, Florida |