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delusional

adj. · n.
US //dɪˈɫuʒənəɫ// UK //dɪlˈuːʒənəl// delu·sion·al
  1. 1 having false beliefs (adj.)
    B2 Upper Intermediate

    believing something that is not true, even when there is proof that you are wrong.

    holding idiosyncratic beliefs that are maintained despite being contradicted by reality or rational argument.

    Example

    He was delusional if he thought he could finish the whole project in one day.

    Example

    The CEO's delusional insistence that the company was profitable led to a complete lack of preparation for the upcoming audit.
  2. 2 relating to a medical delusion (adj.)
    C1 Advanced Technical Medicine

    relating to a serious mental health condition where a person cannot tell what is real.

    pertaining to or characterised by clinical delusions as a symptom of a psychiatric disorder.

    Example

    The patient was experiencing delusional thoughts and needed professional help.

    Example

    The psychiatrist noted that the patient's delusional episodes were becoming more frequent and less responsive to the current medication dosage.
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  1. 3 a person with delusions (n.)
    C2 Proficiency Formal

    a person who believes things that are not true.

    an individual suffering from a delusion or a delusional disorder.

    Example

    The book describes the tragic life of a delusional who believed he was a king.

    Example

    In his early essays, the philosopher treats the delusional not as a patient to be cured, but as a subject with a unique perspective on reality.

    Usage

    This noun use is relatively rare and can sound clinical or insensitive; the adjective is much more common.

Origin

From delusion + -al.

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