Where does “dezasseis” come from?

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

Ancestry of “dezasseis”, step by step

dezasseis 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 sex

Step	Language	Word	Meaning
1	Latin	sex	six; 6
2	Proto-Italic	seks	six
3	Proto-Indo-European	swéḱs	six

via Latin ac

Step	Language	Word	Meaning
1	Latin	ac	Alternative form of atque

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