夜更し
よふかし · yofukashi · JLPT N1 · noun
staying up late
🌙 夜 (night) + 更し (change/stretch): you stretch the night, staying up past its usual end
夜更かし means you let the night run longer than it should. Yo (夜) is night, and fukashi (更かし) comes from 更ける, meaning the night deepens toward late hours. Sounds like 'yo-fuka-shi'.
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.
更 — 丙 (bǐng) phonetic + 攴/攵 (action/strike)
Originally an oracle-bone graph showing a hand striking a watch-drum to mark night watches, hence 'to change shifts.' From this came the meanings 'to change' and 'to replace' (gēng). The reading gèng later developed the sense 'further, even more,' as in 'one watch further on.'