用事

1. Origins, structure, and basic meaning

• Structure: 用事(ようじ) is a noun for something one needs to attend to or get done.
• Basic usage: 用事がある says that one has an errand or other business, such as a task at the bank.

2. Common pitfalls and similar expressions

• 済む and 済ませる
  • 用事が済む describes the errand being finished; 用事を済ませる describes someone finishing it. The example's 用事が済んだら makes completion the condition for what follows.
• Compared with 用件
  • 用件(ようけん) identifies the specific matter to convey or handle. While 用事がある says there is something to attend to, 用件を伝える means communicating what that matter is.