Where does “一昨昨日” come from?

一昨昨日 (Japanese) comes from Japanese 一昨日, from Japanese 日, from Old Japanese 日, from Proto-Japonic *pi — day, sun.

一昨昨日 (Japanese): three days ago

Definitions

  1. three days ago

Ancestry of “一昨昨日”, step by step

一昨昨日 traces back through two separate lines of ancestry.

via Japanese 一昨日

StepLanguageWordMeaning
1Japanese一昨日the day before yesterday, two days ago
2Japanese日Sunday
3Old Japanese日the sun; sunlight, sunshine; daytime, daylight
4Proto-Japonic*piday, sun

via Japanese 先

StepLanguageWordMeaning
1Japanese先before, previous; end, tip; earlier, the past
2Middle Chinese先first, former; earlier, first
Every word from Proto-Japonic *pi →Every word from Old Japanese 日 →Every word from Japanese 日 →