Where does “Decembre” come from?

Decembre (Middle English) comes from Old French decembre, from Latin december, from Latin decem, from Latin -nus, from Proto-Italic -nos, from Proto-Indo-European -nós — Creates verbal adjectives from roots.

Ancestry of “Decembre”, step by step

Step	Language	Word	Meaning
1	Old French	decembre	December
2	Latin	december	of December; December
3	Latin	decem	ten; 10
4	Latin	-nus	-an
5	Proto-Italic	-nos	Creates verbal adjectives from verb stems
6	Proto-Indo-European	-nós	Creates verbal adjectives from roots

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