1. Of, relating to, or being a mystery: mysterious and infinite truths.
  2. Simultaneously arousing wonder and inquisitiveness, and eluding explanation or comprehension: a mysterious visitor; mysterious conduct.

[French mystérieux, from mystère, secret, from Latin mystērium. See mystery]

mys·te'ri·ous·ly adv.
mys·te'ri·ous·ness n.

SYNONYMS  mysterious, esoteric, arcane, occult, inscrutable. These adjectives mean beyond human power to explain or understand. Something mysterious arouses wonder and inquisitiveness: “The sea lies all about us.... In its mysterious past it encompasses all the dim origins of life” (Rachel Carson). What is esoteric is mysterious because only a select group knows and understands it: a compilation of esoteric philosophical essays. Arcane applies to what is hidden from general knowledge: arcane economic theories. Occult suggests knowledge reputedly gained only by secret, magical, or supernatural means: an occult rite. Something that is inscrutable cannot be fathomed by means of investigation or scrutiny: “It is not for me to attempt to fathom the inscrutable workings of Providence” (Earl of Birkenhead).

The American Heritage® Dictionary of the English Language, Fourth Edition Copyright © 2004, 2000 by Houghton Mifflin Company. Published by Houghton Mifflin Company. All rights reserved.