Where does “wennen” come from?

wennen (Old Dutch) comes from Proto-Germanic wanjaną, from Proto-Indo-European wenh₁- — to love.

Ancestry of “wennen”, step by step

Step	Language	Word	Meaning
1	Proto-Germanic	wanjaną	to accustom, to make used to
2	Proto-Indo-European	wenh₁-	to love

wennen — Etymology, Origin & Word History | Etymology Explorer