There are four countries with the word Guinea in their names - why? It all traces to a 15th-century Portuguese nickname for the area roughly around where southern Senegal is today (that's from a local self-appellation thought to trace to the Berber word aginaw, meaning "black"). Eventually the definition expanded to include all of the west African coastline, which was then partitioned by the colonial powers into French Guinea, British Guinea, and so on. Finally, many of those countries kept those names when they achieved independence, giving us the states of Guinea, Guinea-Bissau, and Equatorial Guinea. Papua New Guinea got its name from a Spanish explorer in 1545 who likened the skin color of the natives there to that of West Africans, the word guinea meaning "gold coin" was also named after the region in Africa because it was made out of gold extracted from the area, and the guinea pig was named after Guyana, which has a separate origin.
Adam Aleksic, a rising sophomore studying linguistics and government at Harvard University, has been described as the internet's sixth most famous etymologist. He also has disturbing interests in politics, vexillology, geography, board games, conlanging, and law.