| Sort by Entry Name | Sort by Category | Featured Entry |
|---|---|---|
| OB markers | Politics | Yes |
| Oei Hong Leong | People | Yes |
| Ong , Christina | People | Yes |
| open market value | Transport | Yes |
| orchids | Nature | Yes |
| Order of Temasek | Nationhood | Yes |
| Otokichi Yamamoto | History | Yes |
| obesity | Health | No |
| obscenity laws | Legal | No |
| Observatory, The | Arts, Culture and Entertainment | No |
| October Cherries | Arts, Culture and Entertainment | No |
| Odate Shigeo | World War II | No |
| Oddfellows, The | Arts, Culture and Entertainment | No |
| Odeon | Recreation | No |
| Odyssey Dance Theatre | Arts, Culture and Entertainment | No |
| Oehlers, Sir George | History | No |
| Oei Tiong Ham | People | No |
| Off-Peak Car Scheme | Transport | No |
| OG Department Store | Companies | No |
| oil-refining sector | Economy | No |
| Oishi Masayuki, Lieutenant-Colonel | World War II | No |
| Old Admiralty House | Places and Buildings | No |
| Old Chang Kee | Companies | No |
| Old Lines | History, Premodern | No |
| Old Ministry of Labour Building | Places and Buildings | No |
| Old Parliament House and Annexe | Places and Buildings | No |
| Old Thong Chai Medical Institution | Places and Buildings | No |
| Oldham, William | Christianity | No |
| Oliveiro, Douglas | Arts, Culture and Entertainment | No |
| Olympic Games | Sports | No |
| Omar Kampong Melaka Mosque | Islam | No |
| On Shaw Ming | Sports | No |
| Onam | Indian | No |
| one-north | Places and Buildings | No |
| Ong Beng Seng | People | No |
| Ong Eng Guan | History | No |
| Ong Keng Sen | Arts, Culture and Entertainment | No |
| Ong Kim Seng | Arts, Culture and Entertainment | No |
| Ong Lip Tat | People | No |
| Ong Pang Boon | Government | No |
| Ong Poh Lim | Sports | No |
| Ong Siong Kai | People | No |
| Ong Swee Law | People | No |
| Ong Teng Cheong | Presidents | No |
| Ong Tjoe Kim | People | No |
| Ong Wei Soeij | People | No |
| Ong , Remy | Sports | No |
| Operation Cold Store | History | No |
| Operation Jaywick | World War II | No |
| Operation Matador | World War II | No |
| Operation Rimau | World War II | No |
| Operation Tide-Race | World War II | No |
| Operation Zipper | World War II | No |
| opium | History | No |
| Orang Laut | History | No |
| Orchard Cinema | Arts, Culture and Entertainment | No |
| Orchard Road | Places and Buildings | No |
| Orchard Towers | Places and Buildings | No |
| Ord, Colonel Sir Harry | History | No |
| Order of Nila Utama | Nationhood | No |
| Oriental Telephone and Electric Company | History | No |
| OSIM International | Companies | No |
| Othman Wok | Government | No |
| Outram Prison | Places and Buildings | No |
| Outward Bound Singapore | Government | No |
| Ouzo | Headline News | No |
| Oversea-Chinese Banking Corporation | Companies | No |
| Overseas Union Bank | Companies | No |
| Ow Chin Hock | Government | No |
| Owyang, Chi | People | No |
| Owyang, Hsuan | People | No |