'equanimity' originates from Latin, specifically the word 'aequanimitas,' where 'aequus' meant 'equal' and 'animus' meant 'mind or spirit.'

'aequanimitas' transformed into the French word 'équanimité,' and eventually became the modern English word 'equanimity' through Middle English.

Initially, it meant 'evenness of mind or spirit,' and this meaning has largely remained the same in modern usage.