Where does “*dъlžьnъ” come from?

*dъlžьnъ (Proto-Slavic) comes from Proto-Slavic dъlgъ, from Proto-Indo-European *dʰlegʰ-.

Ancestry of “*dъlžьnъ”, step by step

Step	Language	Word	Meaning
1	Proto-Slavic	dъlgъ	debt
2	Proto-Indo-European	*dʰlegʰ-	—

*dъlžьnъ — Etymology, Origin & Word History | Etymology Explorer