English Reference
noun

illusion

n.
US /ˌɪˈɫuʒən/ UK /ɪlˈuːʒən/ il·lu·sion UK spelling illusion's, illusion's

  1. 01 B2 Upper Intermediate

    something that looks or feels different from what it really is.

    an instance of a sensory perception that causes a false interpretation of physical reality.

    Simple

    The mirrors in the small hallway create the illusion of a much larger space.

    In context

    The desert heat created a shimmering optical illusion on the horizon, making the dry road appear as though it were covered in water.

  2. 02 B2 Upper Intermediate

    a false idea or belief that you think is true.

    a persistent false belief or misconception regarding a situation or person.

    Simple

    He was under the illusion that the job would be easy, but it was very hard.

    In context

    The administration maintained the illusion of progress despite mounting evidence that the project was failing to meet its primary objectives.

  3. 03 B2 Upper Intermediate Theatre

    a clever trick performed by a magician to surprise an audience.

    a professional trick or effect performed by an entertainer to deceive the eyes of an audience.

    Simple

    The magician performed a famous illusion where he appeared to float in the air.

    In context

    The stage production relied on sophisticated lighting and hidden mirrors to execute the complex illusion of the protagonist vanishing mid-sentence.

    tricksleight of handstunt

By this point the Moon will be very low in the south-western sky, causing something known as the Moon illusion .

BBC News· 25 Aug 2026

From Old French illusion, from Latin illūsiō, from illūdere, from in- (“at, upon”) + lūdere (“to play, mock, trick”). Displaced native Old English dwimmer.

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

This entry
Origin Latin illūsiō
Level B2 · Upper Intermediate
Frequency Frequent
Updated