Danish Census Book
The first time Tåsinge clearly appears in the sources is in the Danish Census Book from around 1231, where it is called Thosland, and this designation seems to have been in proper use for a very long time, until the Age of Enlightenment, when antiquarians of the day because of the rudimentary state of etymology reinterpreted the name as 'Thorseng' or 'Thorsing', believing the name to mean 'Thors seng' or 'Thors eng' (lit. Thors bed/Thors meadow). This particular change in the island's name was seen in use for more than a century until gradually it changed into the now used form.