In origin it's the same name as Ghana. In the Middle Ages, Arab and Berber traders from North Africa established trade routes through the centre of the Sahara, encountering a rich native state called Ghana. This became an important source of gold in Europe. Later, as Portuguese seafarers explored more of the African coast from Morocco downward, they eventually found a way of getting back home against the prevailing winds, and this enabled them to turn the corner and explore the southern coast of West Africa. Finding the Africans could trade a rich supply of gold, they assumed they had found the coast of Ghana, or Guinea as the Portuguese name was. They founded the fort of Elmina (the mine) on the Gold Coast to profit from this. In fact the Empire of Ghana was entirely inland, and also the gold they produced was alluvial, not mined; but the names have stuck. When the British colony of the Gold Coast became Ghana on independence in 1957, it was a slight misnomer: Ghana was more in what is now Mali.

Furthermore, it is said that lost sailors applied it to a corresponding region of South America, giving rise to the name Guiana. (In fact Guiana might be a local native name meaning "Land of Waters", if a newer dictionary is to be believed.) It is unclear if this confusion resulted in a South American mammal being given the name of Guinea pig. Not content with this lavish toponymy, another island got the name New Guinea some centuries later for no readily apparent reason.

On independence in 1958 the Republic of Guinea was the only French colony not to join the French Community first as an autonomous state: that is, it became fully independent immediately. It was ruled by President Ahmed Sékou Touré for decades; on his death Prime Minister Louis Lansana Béavogui succeeded him, but he was soon overthrown in a military coup by Lansana Conté.

The guinea mentioned in Webster as a British coin last issued in the early 1800s nevertheless continued as a unit of account, even beyond decimalisation (1971). Certain professions continued to charge in guineas: the law, for example, and racing prizes were sometimes expressed in guineas (so you get races named the So-and-so Guineas). It conveyed a kind of big-old-money feel to a transaction. Abbreviation "gn." or "gns.". A guinea being one pound and one shilling, it converted to £1.05 in decimal currency, which did away with all the colourful expressions of old. It died away and is no longer used at all.