宣伝

1. Origins, structure, and basic meaning

• Structure: 宣伝 (せんでん) means publicity or promotion. 宣伝する is a deliberate promotional action; 宣伝になる says something comes to function as publicity.
• Basic usage: A new shop is actively promoted with flyers, while word of mouth becomes its best publicity without being an explicit advertising act.

2. Common pitfalls and similar expressions

• Promotion performed and something becoming publicity
  • 宣伝する foregrounds an intentional agent; in 宣伝になった, 口コミ acquires a promotional role. Keep the action and resulting function distinct.