| October 2003 | Ocean | Occitan language |
| Octal | October | October 25 |
| October 1October 1 is the 274th day of the year (275th in Leap years). There are 91 days remaining. Events 331 BC Alexander the Great defeats Darius III of Persia in the Battle of Arbela 959 Edgar the Peaceable becomes king of all England 965 John XIII becomes Pop | October 28October 28 is the 301st day of the year (302nd in leap years) in the Gregorian Calendar, with 64 days remaining. Events 306 Maxentius is proclaimed Roman emperor. 312 Battle of Milvian Bridge: Constantine the Great defeats the forces of Maxentius. Roman e | October 24October 24 is the 297th day of the year (298th in leap years) in the Gregorian Calendar, with 68 days remaining. Events 69 Second Battle of Bedriacum, forces under Antonius Primus, the commander of the Danube armies, loyal to Vespasian, defeat the forces |
| October 3October 3 is the 276th day of the year (277th in Leap years). There are 89 days remaining in the year. Events 2333 BC Legendary date of the establishment of the Kingdom of Chosun ( Korea) 42 BC First Battle of Philippi: The Triumvirs Mark Antony and Octav | October 17October 17 is the 290th (in leap years the 291st) day of the year according to the Gregorian calendar. There are 75 days remaining. Events 1244 Battle of La Forbie: Crusaders were defeated by Khwarezmians & Egyptians 1346 Battle of Neville's Cross: King D | October 10October 10 is the 283rd day of the year (284th in Leap years). There are 82 days remaining. Events 680 Battle of Karbala: Shia Imam Husayn bin Ali, the grandson of the Prophet Muhammad, was decapitated by forces under Caliph Yazid I. This is commemorated |
| October 26October 26 is the 299th day of the year (300th in leap years) in the Gregorian Calendar, with 66 days remaining. Events 740 An earthquake strikes Constantinople, causing much damage and death. 1640 The Treaty of Ripon is signed, restoring peace between Sc | October 27October 27 is the 300th day of the year (301st in leap years) in the Gregorian Calendar, with 65 days remaining. Events 625 Honorius I becomes Pope. 1644 Second Battle of Newbury in the English Civil War. 1795 The United States and Spain sign the Treaty o | October 29October 29 is the 302nd day of the year (303rd in leap years) in the Gregorian Calendar, with 63 days remaining. Events 437 Valentinian III, Western Roman Emperor, marries Eudoxia, daughter of his cousin Theodosius II, Eastern Roman Emperor in Constantino |
| October 30 | October 31 | October 11 |
| October 20 | October 7 | October 4 |
| Octahedron | Octans | Occult |
| October 14 | October 2 | October 12 |
| October 5 | October 6 | October 8 |
| October 18 | October 9 | October 13 |
| October 15 | October 16 | October 19 |
| October 21 | October 22 | October 23 |
| Octapad | Oceania | OCR |
| Occam | Occam programming language | October Revolution |
| Occidental | Occidental language | Octopus |
| OC-135 Open Skies | Occidental College | Occam's Razor |
| Octave | Octet | Ocaml |
| Oceanography | Occupational therapy | Occupied territories |
| Oceanus | Octonion | Oceanside |
| Ocean thermal energy conversion | Octavia | Oceanid |
| Ochazuke | Ochimus | Ocridion |
| Ocyrhoe | Ocnus | Ocalea |
| Occator | Occupied Japan | Oconto County, Wisconsin |
| Ochiltree County, Texas | Oconee County, South Carolina | Ocean County, New Jersey |
| Ockendon | Oceana County, Michigan | Oconee County, Georgia |
| Oceanus Procellarum | October Crisis | Ochun |
| Occupation | October 2002 | Ocotillo, California |
| Oceanside, California | Oceano, California | Occidental, California |
| Ocean View, Delaware | Ocala, Florida | Ocean Breeze Park, Florida |
| Ocean City, Florida | Ocoee, Florida | Ocean Ridge, Florida |
| Ocilla, Georgia | Ochlocknee, Georgia | Oconee, Georgia |
| Oconee, Illinois | Ocheyedan, Iowa | Ocean City, Maryland |
| Ocean Pines, Maryland | Ocean Grove, Massachusetts | Ocean Bluff-Brant Rock, Massachusetts |
| Oceola Township, Michigan | Ocqueoc Township, Michigan | Ocean Springs, Mississippi |
| Octavia, Nebraska | Oconto, Nebraska | Ocean City, New Jersey |
| Ocean Township, Monmouth County, New Jersey | Ocean Grove, New Jersey | Oceanport, New Jersey |
| Ocean Township, Ocean County, New Jersey | Ocean Acres, New Jersey | Ocean Gate, New Jersey |
| Oceanside, New York | Ocean Beach, New York | Ocean Isle Beach, North Carolina |
| Ocracoke, North Carolina | Octa, Ohio | Ocean City |