noun, adverb
a certain day; one day
Used when the specific date is not named, often in narratives, announcements, or formal writing. Functions as a noun or adverbially.
某日、都内のホテルで会合が開かれた。
On a certain day, a meeting was held at a hotel in Tokyo.
事件は某日午後３時ごろ発生した。
The incident occurred around 3 p.m. on a certain day.