Where does “sibilare” come from?

sibilare (Latin) comes from Latin sībilus, from Proto-Indo-European sweysd- — to hiss.

Ancestry of “sibilare”, step by step

Step	Language	Word	Meaning
1	Latin	sībilus	—
2	Proto-Indo-European	sweysd-	to hiss

sibilare — Etymology, Origin & Word History | Etymology Explorer