'unstrap' originates from the prefix 'un-' meaning 'reverse action' and the word 'strap', which comes from Middle Dutch 'strope', meaning 'a band or strip'.

'strap' changed from the Middle Dutch word 'strope' and eventually became the modern English word 'strap'.

Initially, 'strap' meant 'a band or strip', and 'unstrap' evolved to mean 'to remove or loosen a strap'.