Where does “言わずもがな” come from?

言わずもがな (Japanese) comes from Japanese も, from Old Japanese も, from Proto-Japonic mə, from Arabic مَن — who?; who.

Ancestry of “言わずもがな”, step by step

言わずもがな traces back through two separate lines of ancestry.

via Japanese も

StepLanguageWordMeaning
1JapaneseもUsed to form the conjectural form of verbs,...
2Old Japaneseもnon-unique topic marker: also, even
3Proto-Japonicmənon-unique topic marker: also, even, too, as well
4Arabicمَنwho?; who

via Japanese かな

StepLanguageWordMeaning
1Japaneseかなexpresses wonder or postulation on the part of...
2Old Japaneseかな—
Every word from Arabic مَن →Every word from Proto-Japonic mə →Every word from Old Japanese も →