Where does “sleng-” come from?

sleng- (Proto-Indo-European) comes from Proto-Indo-European sel-, from Proto-Indo-European ser- — to flow; to guard; to bind, to tie together.

Ancestry of “sleng-”, step by step

Step	Language	Word	Meaning
1	Proto-Indo-European	sel-	dwelling; piece of wood; beam, post, balk, board,...
2	Proto-Indo-European	ser-	to flow; to guard; to bind, to tie together

sleng- — Etymology, Origin & Word History | Etymology Explorer