unknowable (adj.)

• able
• ambiguous
• arcane
• cabalistic
• enigmatic
• impenetrable
• inarticulate
• incalculable
• incognizable
• incoherent
• incomprehensible
• inscrutable
• mysterious
• mystic
• numinous
• puzzling
• rambling
• sealed
• strange
• unapparent
• unbeknown
• uncharted
• unclassified
• unconnected
• undisclosed
• undiscoverable
• undiscovered
• unexplained
• unexplored
• unfamiliar
• unfathomable
• unfathomed
• unheard
• unheard-of
• unidentified
• unimaginable
• unintelligible
• unknown
• unperceived
• unplumbed
• unrevealed
• unsuspected
• untouched
• virgin