Where does “-th” come from?

-th (Albanian) comes from Proto-Indo-European -ts, from Proto-Indo-European -ḱos — -y, -ic.

Ancestry of “-th”, step by step

Step	Language	Word	Meaning
1	Proto-Indo-European	-ts	—
2	Proto-Indo-European	-ḱos	-y, -ic

-th — Etymology, Origin & Word History | Etymology Explorer