\Blue"beard\, n.
The hero of a medi[ae]val French nursery legend, who, leaving
home, enjoined his young wife not to open a certain room in
his castle. She entered it, and found the murdered bodies of
his former wives. -- Also used adjectively of a subject which
it is forbidden to investigate.

      The Bluebeard chamber of his mind, into which no eye
      but his own must look.                   --Carlyle.