階下

1. Origins, structure, and basic meaning

• Structure: 階下 (かいか) is a noun for downstairs or a lower floor.
• Basic usage: It describes a smell coming from downstairs or returning to the lower floor.
  • 階下から夕食のいい香りがしてきました。 — A delicious smell from dinner drifted up from downstairs.
  • 忘れ物に気づいて階下へ戻りました。 — I remembered something I had left behind and returned to the lower floor.

2. Common pitfalls and similar expressions

• Source and destination
  • 階下から marks the source from which a smell comes, while 階下へ marks the direction or destination of a person's return.