淫行

1. Origins, structure, and basic meaning

• Structure: 淫行（いんこう） refers to sexual conduct characterized as immoral or blameworthy.
• Basic usage: It occurs in contexts that judge sexual behavior negatively, such as an accusation in a novel or a moral precept.

2. Common pitfalls and similar expressions

• A neutral term versus a condemnatory one
  • 性行為 is a neutral term for sexual activity itself.
  • 淫行 carries condemnation or a negative judgment.