Where does “должно” come from?

должно (Russian) comes from Russian до́лжный, from Proto-Slavic *dъlžьnъ, from Proto-Slavic dъlgъ, from Proto-Indo-European *dʰlegʰ- — to owe, be indebted to.

должно (Russian): it must be, probably

Definitions

  1. it must be, probably

Ancestry of “должно”, step by step

StepLanguageWordMeaning
1Russianдо́лжныйdue; required
2Proto-Slavic*dъlžьnъobliged
3Proto-Slavicdъlgъdebt
4Proto-Indo-European*dʰlegʰ-to owe, be indebted to
Every word from Proto-Indo-European *dʰlegʰ- →Every word from Proto-Slavic dъlgъ →Every word from Proto-Slavic *dъlžьnъ →
должно — Etymology, Origin & Word History | Etymology Explorer