Where does “décimo” come from?

décimo (Portuguese) comes from Old Portuguese deçimo, from Latin Decimus, from Latin decem, from Latin -nus, from Proto-Italic -nos, from Proto-Indo-European -nós — Creates verbal adjectives from roots.

décimo (Portuguese): tenth

Definitions

tenth

Ancestry of “décimo”, step by step

Step	Language	Word	Meaning
1	Old Portuguese	deçimo	—
2	Latin	Decimus	originally used for a tenth-born son
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 →