Unexplained

Adjective

 * 1) Not explained. Of unknown cause or origin.

Thesaurus
able, enigmatic, incalculable, incognizable, invisible, mysterious, puzzling, sealed, strange, unapparent, unapprehended, unascertained, unbeknown, uncharted, unclassified, undetected, undisclosed, undiscoverable, undiscovered, undivulged, unexplored, unexposed, unfamiliar, unfathomed, unheard, unheard-of, unidentified, uninvestigated, unknowable, unknown, unperceived, unplumbed, unrevealed, unseen, unsolved, unspied, unsuspected, untouched, untraced, untracked, virgin