Synonyms and related words :
able, behind the curtain, behind the scenes, camouflaged, concealed, disguised, enigmatic, hidden, imperceptible, incalculable, incognizable, indiscernible, insensible, invisible, latent, mysterious, out of sight, puzzling, sealed, secret, sightless, strange, submerged, unapparent, unapprehended, unascertained, unbeheld, unbeholdable, unbeknown, uncharted, unclassified, unconsidered, undescried, undetected, undiscernible, undisclosed, undiscoverable, undiscovered, undivulged, unexplained, unexplored, unexposed, unfamiliar, unfathomed, unheard, unheard-of, unheeded, unidentified, uninvestigated, unknowable, unknown, unmarked, unminded, unmissed, unnoted, unnoticed, unobserved, unperceivable, unplumbed, unrealized, unregarded, unremarked, unrevealed, unseeable, unseen, unsolved, unspied, unsuspected, unthought-of, untouched, untraced, untracked, unviewed, unwitnessed, viewless, virgin