This would seem to be Old Faroese for sheep letter.

Does anybody know of any cognates in Old Norse, Modern Icelandic or Swedish for the first part of this compound, please?

This is also an interesting link for the new course:

http://www.tourist.fo/gb/tourism/themes/theme3/theme_3.htm

The Seyðabrævið, or Sheep Letter, is a compilation of laws governing Faroese agriculture promulgated by Hákon of Norway on 28 June 1298.  There are only ......

Cheers,

Simon