What is "glass delusion"

n. (context historical English) The psychological/psychiatric delusion that one is made of glass and will shatter if one sits on a hard surface or is strike.

The glass delusion is an external manifestation of a psychiatric disorder recorded in Europe mainly in the late Middle Ages and early modern period (15th to 17th centuries). People feared that they were made of glass “and therefore likely to shatter into pieces”. One famous early sufferer was King Charles VI of France who refused to allow people to touch him, and wore reinforced clothing to protect himself from accidental “shattering”.