Where does “七日熱” come from?

七日熱 (Japanese) comes from Japanese 病み.

Ancestry of “七日熱”, step by step

七日熱 traces back through two separate lines of ancestry.

via Japanese 病み

StepLanguageWordMeaning
1Japanese病み

via Japanese 七日

StepLanguageWordMeaning
1Japanese七日the seventh day of the month
Every word from Japanese 病み