Latin word undecim comes from Latin unum, Latin decem ((cardinal) ten; 10.), Proto-Indo-European *óynom déḱm̥t

Detailed word origin of undecim

Dictionary entry	Language	Definition
unum	Latin (lat)
decem	Latin (lat)	(cardinal) ten; 10.
*óynom déḱm̥t	Proto-Indo-European (ine-pro)
*oinodecem	Latin (lat)
undecim	Latin (lat)	(cardinal) eleven; 11.

Words with the same origin as undecim