closed book

• Assunto, pessoa ou coisa difícil de entender, conhecer ou interpretar; algo completamente desconhecido ou misterioso para alguém.

A subject, person, or topic that is difficult to understand, know about, or interpret; something that is completely unknown or mysterious to someone.

1. Mystery or unknownB2informal

   A subject or person that is difficult to understand or know about.

   Mistério ou incógnita

   • His past is a closed book to everyone.
   • Quantum physics is a closed book to me.
   • She remains a closed book, even to her closest friends.

2. Finished matterB2informal

   A topic or issue that is no longer being considered or discussed.

   Assunto encerrado

   • That argument is a closed book; let's move on.
   • The investigation is now a closed book.
   • For the team, last season's failure is a closed book.