Question

What is sovereignty?which country has sovereignty over the only large political unit on the south american continent that is not a country? what is that unit?

Answer 1

Sovereignty refers to the right that confers the authority to rule over a certain territory.

The question refers to France, which has sovereignty to rule in their department in South America, know as the French Guiana, which is a region of France and therefore part of the European Union. Since the independence of Belice in 1981, this is the only mainland  American territory which is still part of a European country.