巣穴

1. Origins, structure, and basic meaning

• Structure: 巣穴(すあな) combines 巣, an animal's nest or home, with 穴, a hole, to mean a den or nesting hole.
• Basic usage: It can refer to a fox's den or a bird's nesting hole in a cliff.

2. Common pitfalls and similar expressions

• Dens and nests
  • 巣(す) covers nests and animal homes more broadly, while 巣穴 focuses on a hole used as a home.