Where does “ljunken” come from?

ljunken (Old Danish) comes from Old Norse ljumka, from Proto-Germanic hlēwanōną, from Proto-Indo-European ḱal(w)e-.

Ancestry of “ljunken”, step by step

Step	Language	Word	Meaning
1	Old Norse	ljumka	—
2	Proto-Germanic	hlēwanōną	to make warm
3	Proto-Indo-European	ḱal(w)e-	—

ljunken — Etymology, Origin & Word History | Etymology Explorer