遺憾

1. Origins, structure, and basic meaning

• Structure: 遺憾 is read as いかん and is a formal evaluative noun used predicatively in 誠に遺憾です and in the noun phrase 遺憾の意.
• Basic usage: It expresses official regret about an undesirable outcome such as failed agreement or a rule violation.

2. Common pitfalls and similar expressions

• Register
  • It fits formal statements more than casual disappointment.
• Fixed expression
  • 遺憾の意を示す means to express regret; the phrase alone does not necessarily amount to an apology or admission of responsibility.