Fehmern Femern, or Fehmarn, an island of Prussia, in the province of Schleswig-Holstein,-separated from Holstein by the Fehmarn sound, and from the Danish island of Laaland by the Fehmarn belt, 37 in. E. N. E. of Kiel; area, about 70 sq. m.; pop. about 10,000. It is accessible only to small boats, owing to the shallowness of the sea. The principal products are grain and peas. There is an active trade in woollen hosiery, and a number of the inhabitants are also engaged in fishing. Capital, Burg or Borg.-Femern was taken in 1420 by King Eric of Denmark, who had all the young women slain on the so-called Maiden mountain, near the village of Petersdorf. It was recovered by the duke of Holstein in 1426. The treaty of Flensburg, 1580, gave the island to the Gottorp line of dukes, with whom it passed to Denmark two centuries afterward. Femern was taken by Prussia in March, 1864, during the war with Denmark.