Emily Dickinson Lexicon

MYS'TER-Y, n. [L. mysterium, Gr. μυστηριον, a secret. This word in Greek is rendered also murium latibulum; but probably both senses are from that of hiding or shutting; μυω, to shut, to conceal.]

1. A profound secret; something wholly unknown or something kept cautiously concealed, and therefore exciting curiosity or wonder; such as the mystery of the man with the iron mask in France.
2. In religion, any thing in the character or attributes of God; or in the economy of divine providence, which is not revealed to man; President Moore.
3. That which is beyond human comprehension until explained. In this sense, mystery often conveys the idea of something awfully sublime or important; something that excites wonder. Great is the mystery of godliness. 1 Tim. ill. Having made known to us the mystery of his will. Eph. i. We speak the wisdom of God in a mystery. 1 Cor. ii.
4. An enigma; any thing artfully made difficult
5. A kind of ancient dramatic representation. Bp. Percy.
6. A trade; a calling; any mechanical occupation which supposes skill or knowledge peculiar to those who carry it on, and therefore a secret to others. [The word in the latter sense has been supposed to have a different origin from the foregoing, viz. Fr. metier, Norm. mestier, business, trade, occupation, as if from Norm. mestie, master. But this is probably incorrect.]
7. A kind of old play.