Dictionary.com
Thesaurus.com
Synonyms

mysterious

American  
[mi-steer-ee-uhs] / mɪˈstɪər i əs /

adjective

  1. full of, characterized by, or involving mystery.

    a mysterious occurrence.

    Synonyms:
    cryptic, occult, esoteric, secret
  2. implying or suggesting a mystery.

    a mysterious smile.

  3. of obscure nature, meaning, origin, etc.; puzzling; inexplicable.

    a mysterious inscription on the ancient tomb.

    Synonyms:
    impenetrable, enigmatic, incomprehensible, unintelligible, unfathomable

mysterious British  
/ mɪˈstɪərɪəs /

adjective

  1. characterized by or indicative of mystery

  2. puzzling, curious, or enigmatic

"Collins English Dictionary — Complete & Unabridged" 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Related Words

Mysterious, inscrutable, mystical, obscure refer to that which is not easily comprehended or explained. That which is mysterious, by being unknown or puzzling, excites curiosity, amazement, or awe: a mysterious disease. Inscrutable applies to that which is impenetrable, so enigmatic that one cannot interpret its significance: an inscrutable smile. That which is mystical has a secret significance, such as that attaching to certain rites or signs: mystical symbols. That which is obscure is discovered or comprehended dimly or with difficulty: obscure motives.

Other Word Forms

  • mysteriously adverb
  • mysteriousness noun
  • quasi-mysterious adjective
  • quasi-mysteriously adverb
  • unmysterious adjective
  • unmysteriously adverb
  • unmysteriousness noun

Etymology

Origin of mysterious

First recorded in 1610–20; mystery 1 + -ous

Example Sentences

Examples are provided to illustrate real-world usage of words in context. Any opinions expressed do not reflect the views of Dictionary.com.

So the Sora video-generating app was canceled, and my guess is the Atlas browser—plus a mysterious hardware device by designer diva Jony Ive—may be the next to be killed.

From The Wall Street Journal • Mar. 29, 2026

The regulatory filing also disclosed that a mysterious bidder had surfaced at the auction’s 11th hour.

From Los Angeles Times • Mar. 26, 2026

Ursula has shades of Gellar’s famous characters — Buffy’s physical ferocity, Kathryn Merteuil’s ruthless cattiness, Daphne Blake’s affinity for mysterious games — but doesn’t play to one exclusively.

From Salon • Mar. 26, 2026

Researchers have uncovered how a mysterious ion channel helps cells break down waste, opening new possibilities for treating Parkinson's disease.

From Science Daily • Mar. 26, 2026

Now, at home, Powers told his wife about the mysterious meeting in cottage 1.

From "Fallout: Spies, Superbombs, and the Ultimate Cold War Showdown" by Steve Sheinkin