Where does “decem et septem” come from?

decem et septem (Latin) comes from Latin decem, from Latin -nus, from Proto-Italic -nos, from Proto-Indo-European -nós — Creates verbal adjectives from roots.

decem et septem (Latin): seventeen; 17

Definitions

seventeen; 17

Ancestry of “decem et septem”, step by step

decem et septem traces back through 3 separate lines of ancestry.

via Latin decem

Step	Language	Word	Meaning
1	Latin	decem	ten; 10
2	Latin	-nus	-an
3	Proto-Italic	-nos	Creates verbal adjectives from verb stems
4	Proto-Indo-European	-nós	Creates verbal adjectives from roots

via Latin et

Step	Language	Word	Meaning
1	Latin	et	and; plus; though, even if
2	Proto-Indo-European	éti	beyond; over
3	Proto-Indo-European	h₁é	and, then
4	Proto-Indo-European	ǵʰe	Postpositional intensifying particle: indeed, at any rate, in fact

via Latin Septem

Step	Language	Word	Meaning
1	Latin	Septem	seven; 7
2	Proto-Italic	septem	seven
3	Proto-Indo-European	septḿ̥	seven

Every word from Proto-Indo-European -nós →Every word from Latin -nus →Every word from Latin decem →