Uncertain. The word is, of course, comparable to synonymous German Knödel, but Middle High German knödel yields Moselle Franconian *Knedel, which is very rare at most, and Ripuarian Knöddel, which means “knot, clump”. Knudel, Knidel require Middle High German long vowels (i.e. *knōdel and *knœdel, respectively). Moreover, the gender does not match.
It cannot be ruled out that the word for “dumpling” was borrowed from southern dialects regarding the fact that this dish is more typical of southern German cuisine than northern German. On the other hand, the diversity of interrelated kn-words (compare Knodde, Knöddel, Knuddel, Knöppel, etc.) makes a neat distinction between individual forms impossible and provides for constant innovation.
Knudel f (plural Knudele, diminutive Knüdelche or Knidelche)