Closed Book Definition
noun
One that cannot be known or understood.
American Heritage
(idiomatic) A person or thing that cannot be easily understood; someone or something incomprehensible or puzzling.
adjective
Referring to exams in which external resources such as glossaries, study notes, calculators, etc are prohibited.
Wiktionary
Other Word Forms of Closed Book
Noun
Singular:
closed book
Plural:
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