日夜
にちや · nichiya · JLPT N1 · adverb
day and night
🌞🌙 日 (day, sun) + 夜 (night) = day and night together, meaning always
日 means day or sun and 夜 means night. Joined, they cover the whole span of day and night, so the word means always.
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'.
夜 — 亠 lid + 亻 person + 夕 evening moon
夜 originally depicted a person (亻) under a roof (亠) with the moon (夕) beside them, evoking nighttime rest. The moon component 夕 carries the meaning of evening, while the surrounding elements set the scene of a person at night. Over time it came to mean 'night' in general.