- a former state in N French Indochina, now part of Vietnam.
- Gulf of, an arm of the South China Sea, W of Hainan. 300 miles (485 km) long.
- a former state of N French Indochina (1883–1946), on the Gulf of Tonkin: forms the largest part of N Vietnam
- Gulf of Tonkin an arm of the South China Sea, bordered by N Vietnam, the Leizhou Peninsula of SW China, and Hainan Island. Length: about 500 km (300 miles)