'spontaneity' originates from Latin, specifically the word 'spontaneitas,' where 'spontaneus' meant 'of one's free will.'

'spontaneitas' transformed into the French word 'spontanéité,' and eventually became the modern English word 'spontaneity' through Middle English.

Initially, it meant 'of one's free will,' but over time it evolved into its current meaning of 'voluntary or undetermined action or movement.'