Krakatoa Volcanic Island, Indonesia

Onomatopoeia, imitating the noise made by cockatoos (Kakatoes) which used to inhabit the island. However, Van den Berg points out that these birds are found only in the "eastern part of the archipelago" (meaning the Lesser Sundas, east of Java).
From Sanskrit karka or karkata or karkataka, meaning "lobster" or "crab". (Rakata also means "crab" in the older Javan language.) This is considered the most likely origin.
The closest Malay word is kelakatu, meaning "white-winged ant". Furneaux points out that in pre-1883 maps, Krakatoa does somewhat resemble an ant seen from above, with Lang and Verlaten lying to the sides like wings.
Van den Berg (1884) recites a story that Krakatau was the result of a linguistic error. According to the legend, a visiting ship's captain asked a local inhabitant the island's name, and the latter replied, "Kaga tau" (Aku enggak tahu)—a Jakartan/Betawinese slang phrase meaning "I don't know". This story is largely discounted; it closely resembles other linguistic myths about the origin of the word kangaroo and the name of the Yucatán Peninsula.