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dementia

n.
US //dɪˈmɛnʃiə// UK //dɪmˈɛnʃɐ// de·men·tia
  1. 1 medical condition (n.)
    B2 Upper Intermediate Medicine

    a condition where the brain stops working properly, making it hard to remember things, think clearly, or speak.

    a progressive decline in cognitive function due to brain damage or disease, affecting memory, attention, and problem-solving. Uncountable in general usage; often used with 'vascular' or 'senile' as modifiers.

    Example

    The family noticed the early signs of dementia when he started forgetting where he lived.

    Example

    Recent clinical studies suggest that early intervention can significantly improve the quality of life for patients diagnosed with vascular dementia.

    Usage

    Often used as an uncountable noun, though specific types are referred to as 'dementias'.
    • cognitive decline
    • alzheimer's
  2. 2 madness (n.)
    C2 Proficiency Archaic Literary

    an old-fashioned word for being crazy or losing your mind.

    a state of madness or insanity. This sense is largely historical and rarely appears in modern clinical or legal contexts.

    Example

    In the old story, the king fell into a deep dementia after losing his crown.

    Example

    The poet described a world descending into a collective dementia, where reason was abandoned for chaos.

    Teacher's tip

    This sense is archaic; in modern English, 'dementia' is almost exclusively a medical term for cognitive decline in the elderly.
Origin

Borrowed from Latin dementia.

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

Last updated June 20, 2026