An Etymological Dictionary of Astronomy and Astrophysics
English-French-Persian

1) Anything that is kept → secret or remains unexplained or unknown.
2) Obscure, puzzling, or → mysterious quality or character (Dictionary.com).

M.E. mysterie, from L. mysterium "secret rite, secret worship; a secret thing," from Gk. mysterion "secret rite or doctrine," from mystes "one who has been initiated," from myein "to close, shut."

Šârdé, from Laki šârd "concealed, hidden, secret," âšârden "to hide, conceal;" cf. Kurd. hašâr, hâšâr "hidden, concealed," šârdinawa, šârây "to hide," Kâzeruni ker "hidden," Av. sar- "shelter;" Proto-Ir. *sar- "to conceal, hide;" Skt. śárman- "cover, protection;" L. celare "to conceal from view;" Goth. huljan "to cover, conceal;" O.H.G. helan "to hide;" E. helmet; PIE *kel- "to conceal, hide, cover."