Where does “prostovan” come from?

prostovan (Romanian) comes from Romanian prost, from Old Church Slavonic простъ, from Proto-Slavic prostъ, from Proto-Indo-European pro-sth₂o-.

Ancestry of “prostovan”, step by step

StepLanguageWordMeaning
1Romanianprostsimple, simple-minded; stupid; poor
2Old Church Slavonicпростъsimple, free, straight
3Proto-Slavicprostъsimple, straight
4Proto-Indo-Europeanpro-sth₂o-—
Every word from Proto-Indo-European pro-sth₂o- →Every word from Proto-Slavic prostъ →Every word from Old Church Slavonic простъ →