月日
つきひ · tsukihi · JLPT N2 · noun
years
🌙☀️ 月 (moon) + 日 (sun/day) = moon and sun taking turns, so their pair marks time passing
The moon sets the month and the sun sets the day, so the pair 月日 stands for time itself. Read it as moon plus sun and the meaning time, years, or days follows.
月 — pictograph of crescent moon
月 is a pictograph of a crescent moon, chosen over a full circle to distinguish it from 日 (sun). The inner strokes originally depicted the moon's shadow or markings. As a radical it often relates to the moon, time, or (via a lookalike form of 肉 'flesh') body parts.
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'.