'impassive' originates from Latin, specifically the word 'impassivus', where 'im-' meant 'not' and 'passivus' meant 'suffering or feeling'.

'impassivus' transformed into the French word 'impassif', and eventually became the modern English word 'impassive' through Middle English.

Initially, it meant 'not suffering or feeling', but over time it evolved into its current meaning of 'not showing emotion'.