Where does “dertiene” come from?

dertiene (Middle Dutch) comes from Old Dutch thritēn, from Proto-Germanic þritehun, from Proto-Germanic tehun, from Proto-Indo-European déḱm̥t — ten.

Ancestry of “dertiene”, step by step

Step	Language	Word	Meaning
1	Old Dutch	thritēn	—
2	Proto-Germanic	þritehun	thirteen
3	Proto-Germanic	tehun	ten
4	Proto-Indo-European	déḱm̥t	ten

dertiene — Etymology, Origin & Word History | Etymology Explorer