Where does “Kongojoki” come from?

Kongojoki (Finnish) comes from Finnish joki, from Finnish sokeus, from Finnish sokea, from Proto-Finnic sokeda — blind.

Ancestry of “Kongojoki”, step by step

Kongojoki traces back through two separate lines of ancestry.

via Finnish joki

StepLanguageWordMeaning
1Finnishjokiriver
2Finnishsokeusblindness
3Finnishsokeablind
4Proto-Finnicsokedablind

via Finnish Kongo

StepLanguageWordMeaning
1FinnishKongo—
2FrenchCongoCongo
Every word from Proto-Finnic sokeda →Every word from Finnish sokea →Every word from Finnish sokeus →