A name after a place
Traditional place names are based on words that were used at the time when the name was given. Even if a word in such a name has disappeared later, the name continues to exist and fulfill its function.
Places that are important for moving about, e.g., waterways, were the first places to receive names. For example, the name Päijänne (a lake), the origins of which have faded away, is one of the oldest place names in Finland.
The name Taivassalo in Jämsä used to be Taivalsalo. The original name came from the narrow isthmus in the middle of the island, taival, “a passage”. People could drag their boats over the passage from one bay to the other. The other part of the name, salo, refers to an island.
There are several explanations for the origins of the name Päijänne, but none of them are credible in the light of present-day studies. Since there are a large number of Saami-language names in the Päijänne region, it is very likely that the name Päijänne used to be a word of one of the Saami languages at some stage of its history.