English Reference
adjective

mysterious

adj.
US /mɪˈstɪɹiəs/ UK /mɪstˈiəɹɪəs/ mys·te·ri·ous

  1. 01 B1 Intermediate

    strange, unknown, or difficult to understand or explain.

    relating to or being a mystery; difficult or impossible to understand, explain, or identify.

    Simple

    A mysterious light appeared in the sky late last night.

    In context

    The detectives were baffled by the mysterious disappearance of the painting, as the security alarms had never been triggered.

  2. 02 B2 Upper Intermediate

    behaving in a way that shows you are keeping a secret.

    deliberately enigmatic or evasive in behavior or speech, often to provoke interest or hide information.

    Simple

    He was being very mysterious about where he went last weekend.

    In context

    She gave him a mysterious smile and refused to say another word about her plans for the upcoming merger.

    Usage

    often used to describe a person's expression or tone of voice

Hearing about fields full of dead caterpillars enveloped in a mysterious white substance intrigued the South African scientist Letodi Luki Mathulwe.

The Guardian· 12 Aug 2026

Football is fertile ground for stories of mysterious forces, blamed for everything from missed penalties to decades of failure .

The Guardian· 9 Aug 2026

From Middle English *misterius (implied in misteriusly), probably partly from Middle French mystérieux and partly from Latin mystērium + -ous. By surface analysis, mystery + -ous.

Etymology adapted from Wiktionary, available under CC BY-SA 4.0.

This entry
Origin frm mystérieux
Level B2 · Upper Intermediate
Frequency Common
Updated