'afire' originates from Old English, specifically the word 'on fȳr', where 'on' meant 'in' and 'fȳr' meant 'fire'.

'on fȳr' changed from Old English to Middle English 'a fier' and eventually became the modern English word 'afire'.

Initially, it meant 'in a state of burning', and this meaning has largely remained the same in modern usage.