References
- Baumgartner, Emmanuèle, and Philippe Ménard. 1996. Dictionnaire étymologique et historique de la langue française [French Etymological and Historical Dictionary]. Paris: Le Livre de Poche.
- Den store danske Encyklopædi [The Great Danish Encyclopedia]. 1996. Volume 6, Erna—fraktur [Erna-fracture]. Copenhagen: Gyldendal.
- Katlev, Jan, ed. 2000. Politikens Etymologisk Ordbog [Politiken's Etymological Dictionary]. Copenhagen: Politiken.
- Little, William. 1967. The Shorter Oxford English Dictionary on Historical Principles Volume 1, A-M. Oxford: Clarendon Press.