mystery

n. (pl. -ies) 1 secret, hidden, or inexplicable matter. 2 secrecy or obscurity. 3 (attrib.) Secret, undisclosed (mystery guest). 4 practice of making a secret of things (engaged in mystery and intrigue). 5 (in full mystery story) fictional work dealing with a puzzling event, esp. A murder. 6 a religious truth divinely revealed. 7 (in pl.) A secret religious rites of the ancient greeks, romans, etc. B archaic eucharist. [greek musterion: related to *mystic]

a. A profound secret; something wholly unknown, or something kept cautiously concealed, and therefore exciting curiosity or wonder; something which has not been or can not be explained; hence, specifically, that which is beyond human comprehension.