昔日
xī rì · HSK 7
day
📜 昔 (past) + 日 (day) = days of the past, i.e. former times
昔 already means former or bygone, and 日 means day; together 昔日 names the days that are gone. The 日 sun radical also sits inside 昔, doubling down on the time-of-day sense.
日 — pictograph of the sun
日 is a pictograph of the sun, originally drawn as a circle with a dot or stroke inside representing the sun's substance. Over time the round shape was squared off into the modern rectangular form. It means 'sun' and by extension 'day'.