終日
しゅうじつ · shuujitsu · JLPT N1 · noun
day
☀️ 终日 (しゅうじつ) = whole day: 終 end + 日 day; the day from start to end
終 means 'end' and 日 means 'day', so 終日 is the whole span from the day's beginning to its end. Read shuu-jitsu as 'shoe-jeet': the sun runs all day.
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'.