Where does “ondze” come from?

ondze (Old Spanish) comes from Latin undecim, from Latin oinodecem, from Proto-Indo-European óynom déḱm̥t.

Ancestry of “ondze”, step by step

Step	Language	Word	Meaning
1	Latin	undecim	eleven; 11
2	Latin	oinodecem	—
3	Proto-Indo-European	óynom déḱm̥t	—

ondze — Etymology, Origin & Word History | Etymology Explorer