Definition of a closed book
- Even to his closest friends, he was always something of a closed book.
: not open
: composed entirely of closed tubes or vessels
: a set of written sheets of skin or paper or tablets of wood or ivory
: a set of written, printed, or blank sheets bound together between a front and back cover
: a long written or printed literary composition
: to register (something, such as a name) for some future activity or condition (as to engage transportation or reserve lodgings)
: to schedule engagements for
: to set aside time for
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