Where does “viginti” come from?

viginti (Latin) comes from Latin quīnque, from Proto-Italic kʷenkʷe, from Proto-Indo-European pénkʷe — five.

Ancestry of “viginti”, step by step

Step	Language	Word	Meaning
1	Latin	quīnque	—
2	Proto-Italic	kʷenkʷe	five
3	Proto-Indo-European	pénkʷe	five

viginti — Etymology, Origin & Word History | Etymology Explorer