Synonyms and related words :
able, enigmatic, incalculable, incognizable, invisible, mysterious, puzzling, sealed, strange, unapparent, unapprehended, unascertained, unbeknown, uncharted, unclassified, unconsidered, undetected, undisclosed, undiscoverable, undiscovered, undivulged, unexamined, unexplained, unexposed, unfamiliar, unfathomed, unheard, unheard-of, unidentified, uninvestigated, unknowable, unknown, unperceived, unplumbed, unrevealed, unscanned, unsearched, unseen, unsifted, unsolved, unspied, unstudied, unsuspected, untouched, untraced, untracked, unweighed, virgin