'unrestrained' originates from the prefix 'un-' meaning 'not' and the word 'restrain' from Latin 'restringere', where 're-' meant 'back' and 'stringere' meant 'to bind'.

'restrain' changed from the Old French word 'restraindre' and eventually became the modern English word 'restrain'.

Initially, it meant 'to bind back or hold back', but over time it evolved into its current meaning of 'not controlled or held back'.