1.
unknown, unidentified, unascertained
Indicates that information such as a person's identity, date, cause, or details is not known or cannot be confirmed. A formal term used in official records and reports.
A formal, written-register word. Typically placed after the noun it modifies in the pattern 〜不詳 (~ unknown). Common in police reports, medical records, historical documents, and news articles. Unlike 不明 (unclear, unknown), which is used more broadly, 不詳 specifically implies that details have not been ascertained or verified.