'Congo-Brazzaville' is formed from 'Congo' and 'Brazzaville'. 'Congo' ultimately comes from the name of the Kongo people/kingdom (from Kikongo 'Kongo'). 'Brazzaville' is named after the explorer Pierre Savorgnan de Brazza.

'Congo' was originally the name of the Kongo kingdom and the river; it became the name for the surrounding region and later the modern states. 'Brazzaville' originated from the surname 'Brazza' (Pierre Savorgnan de Brazza) and was applied to the town founded near the Congo River. The hyphenated form 'Congo-Brazzaville' developed in English usage to distinguish the Republic of the Congo from the Democratic Republic of the Congo.

Initially 'Congo' referred to the Kongo people/kingdom (the people and their territory); over time it became the name of a river, a region, and then one or more modern states. Adding 'Brazzaville' became a practical way to specify the Republic of the Congo (the state whose capital is Brazzaville).