忍び

1. Origins, structure, and basic meaning

• Structure: In 忍び (しのび), stealth 忍 plus nominal び forms a noun for ninja or stealth.
• Basic usage: 忍び can denote a ninja or stealthy person, while お忍びで idiomatically describes going somewhere privately or incognito.

2. Common pitfalls and similar expressions

• Ninja and お忍び
  • The person noun and adverbial expression have different roles.