closed book
Unknowable to outsiders
A closed book is something or someone that remains mysterious, inaccessible, or impossible to understand: Quantum physics is a closed book to me.
The metaphor suggests information that exists but can't be accessed—pages you're unable to read.
The opposite is an open book, someone transparent and easily understood.
Something unexplained or unknown
- enigmaSomething hard to fathom
- inscrutableImpossible to understand
- incomprehensibleImpossible to understand
- impenetrableImpossible to pass through
opaque · unfathomable · puzzle · riddle · conundrum · cryptic · arcane · obscure
Restricted to certain parties
- guardedWary and restrained
- reservedRestrained in manner
- tight-lippedUnwilling to divulge
- uncommunicativeUnwilling to share thoughts
withdrawn · discreet · reticent · secretive · poker-faced · cagey · evasive · unforthcoming
Made invisible deliberately
- veiledConcealed or obscured
- shroudedCovered and hidden
- maskedHaving face covered
- unrevealedNot made public
undisclosed · covert · camouflaged · buried · obscured · unspoken · unshared · under wraps
Impossible to access or befriend
- unreachableCannot be accessed
- exclusiveLimited to one group
- restrictedLimited in scope
- forbiddenNot allowed
off-limits · sealed · shut · locked · barred · impervious · unwelcoming · standoffish
Not yet utilized
- undiscoveredNot yet found
- latentPresent but inactive
- dormantInactive but capable
- unrealizedNot made actual
undeveloped · unwritten · blank slate · unexplored · uncharted · waiting · promise · possibility
Evaluative examination
- assessmentFormal evaluation of worth
- memorizationCommitting information to recall
- recallMemory retrieval act
- unpreparedLacking readiness beforehand
final exam · study · cram · retention · rote learning · unaided
mystery
Something unexplained or unknown
- enigmaSomething hard to fathom
- inscrutableImpossible to understand
- incomprehensibleImpossible to understand
impenetrable · opaque · unfathomable · puzzle · riddle · conundrum · cryptic · arcane · obscure · unreadable
private
Restricted to certain parties
- guardedWary and restrained
- reservedRestrained in manner
- tight-lippedUnwilling to divulge
uncommunicative · withdrawn · discreet · reticent · secretive · poker-faced · cagey · evasive · unforthcoming · buttoned-up
concealed
Made invisible deliberately
unrevealed · undisclosed · covert · camouflaged · buried · obscured · unspoken · unshared · under wraps
unapproachable
Impossible to access or befriend
- unreachableCannot be accessed
- exclusiveLimited to one group
- restrictedLimited in scope
forbidden · off-limits · sealed · shut · locked · barred · impervious · unwelcoming · standoffish · aloof
untapped
Not yet utilized
- undiscoveredNot yet found
- latentPresent but inactive
- dormantInactive but capable
unrealized · undeveloped · unwritten · blank slate · unexplored · uncharted · waiting · promise · possibility
test
Evaluative examination
- assessmentFormal evaluation of worth
- memorizationCommitting information to recall
- recallMemory retrieval act
unprepared · final exam · study · cram · retention · rote learning · unaided
- teststest, tests, exam, exams, quiz
- assessmentsassessments, evaluation, evaluations, test, tests
- literary idiomscatch-22, red herring, white whale, chapter and verse, same page
- Book Idiomson the same page, same page, turn the page, cover to cover, new chapter
- metaphorsbroken heart, dead metaphor, mixed metaphor, time is money, extended metaphor
- learninglearning, learn, classes, instruction, studying
closed bookopen book
One easily understood
transparent · crystal clear · forthcoming · candid · plain as day
closed bookopen book
One easily understood
known quantity · second nature · old hat · bread and butter · area of expertise
close, book, closet, books, closed, closing, bookish, closure, enclosure