
1) Gulf of the South China Sea 2) Northern region of Vietnam 3) Part of french indochina 4) Region of french indochina
Found on
https://www.crosswordclues.com/clue/tonkin

Tonkin (Bắc Kỳ, historically Đàng Ngoài), also spelled Tongkin, Tonquin or Tongking, is the northernmost part of Vietnam, south of China`s Yunnan and Guangxi Provinces, east of northern Laos, and west of the Gulf of Tonkin. `Tonkin` is a corruption of Đông Kinh (東京), the name of Hanoi during the Lê Dynasty. Locally, Tonkin is know......
Found on
http://en.wikipedia.org/wiki/Tonkin

northern Vietnam during the French colonial period. The term Tonkin was never officially used by the Vietnamese to describe their country.[3 related articles]
Found on
http://www.britannica.com/eb/a-z/t/61
No exact match found.