folie a deux

A folie a deux is a mental disorder that two people share and experience at the same time. If you and your best friend are convinced that her dog can speak English, it may be a folie a deux.

When two people have the identical delusion — believing something is true which clearly could not be — it's called a folie a deux, or sometimes a "shared psychotic disorder." This unusual disorder is more likely to occur in a closely related pair, like twins, or a married couple, who are isolated from other people. Folie à deux means "shared madness," or "madness for two" in French. If three people share the delusion, it's a "folie a trois."

Definitions of folie a deux
  1. noun
    the simultaneous occurrence of symptoms of a mental disorder (as delusions) in two persons who are closely related (as siblings or man and wife)
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    type of:
    disturbance, folie, mental disorder, mental disturbance, psychological disorder
    (psychiatry) a psychological disorder of thought or emotion; a more neutral term than mental illness
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