拡散

1. Origins, structure, and basic meaning

• Structure: 拡散 (かくさん) denotes spread or diffusion and can describe either spontaneous dispersal or deliberate dissemination.
• Basic usage: 香りが拡散した describes scent spreading; 情報を拡散する describes someone disseminating information.

2. Common pitfalls and similar expressions

• Intransitive diffusion and transitive dissemination
  • The spreading substance takes が in the first pattern; deliberate distribution takes its object with を.