Where does “生日” come from?

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

生日 (Japanese): a lucky day, auspicious day; one's birthday

Definitions

  1. a lucky day, auspicious day; one's birthday

Ancestry of “生日”, step by step

生日 traces back through 3 separate lines of ancestry.

via Japanese

StepLanguageWordMeaning
1JapaneseSunday
2Old Japanesethe sun; sunlight, sunshine; daytime, daylight
3Proto-Japonic*piday, sun

via Chinese 生日

StepLanguageWordMeaning
1Chinese生日birthday

via Japanese 生く

StepLanguageWordMeaning
1Japanese生くto live; to exist; to keep alive; to grow or...
Every word from Proto-Japonic *piEvery word from Old Japanese Every word from Japanese
生日 — Etymology, Origin & Word History | Etymology Explorer