"psychological phenomenon that causes a person to see patterns in a random stimulus," considered as a form of perceptual hallucination, by 1867, from German Pareidolie (1866). The elements are an assimilated form of Greek para- "alongside, beyond; irregular, abnormal" (as in paranoid; see para- (1)) + Greek eidolon "appearance, reflection in water or a mirror," also "mental image, apparition, phantom" (see eidolon, which is attested in English by 1881 as "a likeness, an image"). With abstract-noun element -ia.