köken: Univerbation of Zweifels (“of doubt”) + ohne (“without”), from Middle High German zwīvels āne, during which ohne could still take a genitive object: "einer Sache ohne sein".
Esperantosen ia ombro da dubo, sen ombro de dubo, sendube /senˈdube/
undoubtedly
köken: Etymology tree Latin sineder. Esperanto sen Esperanto sen- Esperanto dubo Esperanto -e Esperanto sendube From sen- (“without, -less”) + dubo (“doubt”) + -e (adverbial suffix).