某日

1. Origins, structure, and basic meaning

• Structure: 某日 is read as ぼうじつ and can mean “a certain day” or “one day”, depending on context.
• Basic usage: The examples show a particular day recorded in a diary and an unspecified autumn day when a parcel arrived.

2. Common pitfalls and similar expressions

• Distinguishing senses and uses
  • It is a literary way to withhold the exact date and say a certain day, using 某 as in 某氏 for an unnamed person.