'unblock' originates from the prefix 'un-' meaning 'not' or 'reverse' and the word 'block', which comes from Old French 'bloc', meaning 'log'.

'bloc' transformed into the Middle English word 'blok', and eventually became the modern English word 'block'.

Initially, 'block' meant 'a large solid piece of hard material', but over time it evolved to mean 'an obstruction'. 'Unblock' thus means to remove such an obstruction.