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day; days
sun; sunshine; sunlight
(the) day; daytime; daylight
date; deadline
(past) days; time (e.g. of one's childhood)
case (esp. unfortunate); event
「日」 has other readings with different meanings.
今日は本当に暑い日ですね。
Today is a hot day, isn't it?
日が山の向こうに沈んだ。
The sun sank beyond the mountain.
今日はとても暑い日ですよ。
Today is a very hot day, isn't it?