地下

1. Origins, structure, and basic meaning

• Structure: 地下(ちか) refers to the space below ground or the part of a building below ground level.
• Basic usage: It is used for an underground passage or the location of a basement restaurant.

2. Common pitfalls and similar expressions

• Underground space and a basement room
  • 地下室(ちかしつ) is a room below ground, while 地下 can refer to a broader underground area.
• Adding a floor number
  • 地下一階(ちかいっかい) means the first basement level.