'pain' originates from Old French, specifically the word 'peine', which came via Vulgar Latin from Latin 'poena' where 'poena' meant 'punishment' or 'penalty'.

'poena' in Latin developed into Old French 'peine' (meaning anguish, punishment), then entered Middle English as 'peine'/'pen' and eventually became modern English 'pain'.

Initially it meant 'punishment' or 'penalty' in Latin, but over time it shifted toward the sense of 'suffering' or 'physical/mental hurt' and later also acquired the sense of 'careful effort' (as in 'take pains').