From Low German, corruption of Middle Low German kanin from Middle French connin, see Kaninchen. The R might have intruded the word in the Mecklenburg-Brandenburg area, where rhotic and non-rhotic accents of Low German meet. In the rhotic southern accents, the word probably was pronounced with [äː], a sound absent from the northern dialects, but close to the non-rhotic realisation of /ar/, which is [aː]. The word was thus reanalysed was having /ar/. There are records from the early 20th century of the word being pronounced with [ar] by some Brandenburg citizens, with the presence of the R still being considered a random idiosyncrasy.
Karnickel n (genitive Karnickels, plural Karnickel)
- Karnickel in Duden online