先週

1. Origins, structure, and basic meaning

• Structure: 先週 is a noun read せんしゅう, meaning last week, the week immediately before the current one.
• Basic usage: It can directly mark when an action occurred or modify a later noun through a relative clause.
  • 先週、家族と山へ出かけました。 says that the speaker went to the mountains with family last week; 先週借りた本を明日返す予定です。 says that the book borrowed last week is scheduled to be returned tomorrow.

2. Common pitfalls and similar expressions

• 先週、出かけました
  • This specific relative-time noun can mark the action's time without an added particle.
• 先週借りた本
  • 借りた modifies book, while 先週 states when the borrowing happened.
• 先週 and 今週
  • 先週 is the immediately preceding week, while 今週 is the current week.