This article concentrates on a specific ancient holy word in Finnish and its subsequent development, hiisi. In the Finnish language region hiisi appears as an element in place names in over 230 villages established by the end of the thirteenth century, and at least a majority of these must have existed since prehistoric times. In Finland as well as in Estonia it is possible to demonstrate an earlier sacral function in places which contain hiisi as a component of their name, partly with the help of archeological discoveries, and partly with the help of oral folk tradition. It is particularly among the earliest settlement areas of Southwest Finland, Satakunta and Häme that hiisi features in the names of sacrificial sites or trees, in other wo...