ground · earth

1. Origins, structure, and basic meaning

• Structure: 地 means ground or earth; its on-readings include ち and じ.
• Basic usage: 地下(ちか) means underground or basement, while 地震(じしん) means earthquake. The same character has different readings in these words.

2. Common pitfalls and similar expressions

• An underground passage and a building's basement
  • 地下の通路 is an underground passage, while a building's 地下 can refer to its basement.