'unborrowable' originates from the prefix 'un-' meaning 'not' and the word 'borrow' from Old English 'borgian', meaning 'to lend or borrow'.

'borgian' transformed into the Middle English word 'borwen', and eventually became the modern English word 'borrow'.

Initially, 'borrow' meant 'to lend or borrow', but over time it evolved to specifically mean 'to take and use something belonging to someone else with the intention of returning it'.