Where does “smuk” come from?

smuk (Old Saxon) comes from Proto-Germanic smukkaz, from Proto-Germanic smukkōną, from Proto-Germanic smuknéh₂-.

Ancestry of “smuk”, step by step

Step	Language	Word	Meaning
1	Proto-Germanic	smukkaz	smock, shift, something slipped into
2	Proto-Germanic	smukkōną	to slide into, slip through; to creep, slink
3	Proto-Germanic	smuknéh₂-	—

smuk — Etymology, Origin & Word History | Etymology Explorer