A ghost, phantom, or illusion; something that appears real but isn't actually there.
From Greek phantasma meaning 'phantom' or 'apparition,' derived from phantazein meaning 'to make visible.' This spelling variant is less common than 'phantasm,' though both are used to mean ghostly appearances or tricks of the mind.
Medieval people documented fastsms in tapestries and manuscripts, but we now know many 'ghost sightings' were actually caused by infrasound (very low frequencies below human hearing) that triggers fear and visual hallucinations in our brains.
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