毎日
まいにち · mainichi · JLPT N5 · noun
day
📅 毎日 = 毎 (every) + 日 (day)
毎 (mai) means every, and 日 (nichi) means day or sun. The same 毎 prefix builds 毎週 (every week), 毎月 (every month) and 毎年 (every year), so learning it once unlocks the whole set.
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'.