'phantom' originates from Greek via Late Latin, specifically the Greek word 'phantasma' (through Late Latin 'phantasma'), where 'phantasma' meant 'an apparition, an image'.

'phantasma' (Greek) passed into Late Latin as 'phantasma', then into Old French as 'fantosme'/'fantome', and into Middle English as 'phantom'/'fantome', eventually becoming the modern English word 'phantom'.

Initially, it meant 'an appearance or apparition,' and over time it retained that sense while also extending metaphorically to mean 'an illusion or figment of the mind.'