内緒

1. Origins, structure, and basic meaning

• Structure: 内緒, read ないしょ, means a secret kept from other people.
• Basic usage: It is an everyday word for keeping something from someone or for information known only to two people.

2. Common pitfalls and similar expressions

• Keeping something secret
  • 本人に内緒にする means not telling the person concerned; 二人だけの内緒 is a secret between two people.
• Related words for a secret
  • 内緒 is conversational, while 秘密 has a wider range, from personal secrets to confidential information.