空洞

1. Origins, structure, and basic meaning

• Structure: 空洞(くうどう) is an empty space within an object or underground.
• Basic usage: It is used for a hollow in a tree trunk or a cavity found beneath a road.

2. Common pitfalls and similar expressions

• What is empty compared with 空白
  • 空白(くうはく) can refer to an unwritten part of a page or a gap in a record of time. 空洞 describes an empty space inside an object or underground, as in the examples.