Where does “sonno” come from?

sonno (Old Portuguese) comes from Latin somnium, from Latin somnus, from Proto-Italic swepnos, from Proto-Indo-European swépnos, from Proto-Indo-European swopnos, from Proto-Indo-European swep- — to sleep.

Ancestry of “sonno”, step by step

Step	Language	Word	Meaning
1	Latin	somnium	dream, vision; fantasy, daydream
2	Latin	somnus	sleep; drowsiness, slumber sloth, idleness; death
3	Proto-Italic	swepnos	—
4	Proto-Indo-European	swépnos	sleep, slumber
5	Proto-Indo-European	swopnos	dream
6	Proto-Indo-European	swep-	to sleep

Every word from Proto-Indo-European swep- →Every word from Proto-Indo-European swopnos →Every word from Proto-Indo-European swépnos →