Encyclopedias, Almanacs, Transcripts, and Maps
- Oculo-digito-esophagoduodenal syndrome
- Oculodentodigital Syndrome
- Oculomancy
- Odd-Toed Ungulates: Perissodactyla
- Odén, Svante N. F.(1924-1986)
- Odontology, Historical Cases
- Odor of Sanctity
- Odoric of Pordenone
- Oenomancy
- Oenopides
- Oenopides of Chios
- Oesterreich, Traugott Konstantin(1880-1949)
- Office of Paranormal Investigations
- Office of Research Integrity
- Office of Technology Assessment
- Official UFO (Magazine)
- Ohio Sky Watcher
- Ohm’S Law
- Oil Drilling
- Oil Is Discovered in the Middle East