'unload' originates from the prefix 'un-' meaning 'reverse action' and the word 'load', which comes from Old English 'hladan', meaning 'to load or burden'.

'hladan' transformed into the Middle English word 'loden', and eventually became the modern English word 'load'.

Initially, 'unload' meant 'to remove a load', and this meaning has largely remained the same in modern usage.