The crossword solution for the term CLOSED BOOKS is ENIGMAS. This term refers to books that are not available to the public, such as those that are kept in a library or archive and are not allowed to be taken out. These books may contain valuable information or secrets that are not meant to be shared with the general public. ENIGMAS is an appropriate term to describe these books, as they often contain puzzles or riddles that must be solved in order to gain access to their contents.