Where does “lēiw-i-” come from?

lēiw-i- (Proto-Italic) comes from Proto-Indo-European leh₁y-u- — smooth.

Ancestry of “lēiw-i-”, step by step

Step	Language	Word	Meaning
1	Proto-Indo-European	leh₁y-u-	smooth

lēiw-i- — Etymology, Origin & Word History | Etymology Explorer