pit

1. Origins, structure, and basic meaning

• Structure: 坑 is associated with a pit or mine working; its on-reading is こう.
• Basic usage: 坑内(こうない) means inside a mine, while 坑道(こうどう) means a mine tunnel.

2. Common pitfalls and similar expressions

• An interior location and the passage itself
  • 坑内作業 means work inside a mine. 坑内 identifies the interior space where the work takes place.
  • 狭い坑道 means a narrow mine tunnel. When describing a passage's width or structure, 坑道 names the passage itself.