'phantasmal' originates from Greek, specifically the word 'phantasma', where 'phantasma' meant 'an appearance, image, apparition'.

'phantasmal' changed from Greek 'phantasma' into Late Latin and Medieval Latin 'phantasma', then into Middle English/French forms such as 'fantasm'/'fantasme', and eventually developed into the modern English adjective 'phantasmal' derived from 'phantasm'.

Initially, it meant 'an apparition or visible image', but over time it evolved into the adjective sense 'like an apparition; illusory or ghostlike' used in modern English.