I. Greek. Mysterion--one initiated into the mysteries (at Eleusis)
II. The mystical experience is “a nonintellectual mode of consciousness.[ . . .] It is formless, shapeless, colorless, odorless, soundless. [. . .] It is entirely unlike our everyday consciousness and is wholly incommensurable with it. [. . .] [It] is destitute of any sensations at all.  Nor does it contain any concepts or thoughts.” Walter T. Stace.  The Teachings of the Mystics.
III. Direct knowledge of ultimate Reality can be obtained through subjective experience. 
IV. A sudden, inexplicable understanding of the true meaning of existence. Wordsworth’s “spots of time” or Joyce’s “epiphany,” God manifested in Nature--The sudden perception of the essential meaning of life.
Definitions