'mistakenly-returned' originates from the combination of 'mistakenly' and 'returned', where 'mistakenly' is derived from 'mistake', meaning 'an error or fault', and 'returned' is derived from 'return', meaning 'to go back or come back'.

'mistakenly' evolved from the Old Norse word 'mistaka', meaning 'to take in error', and 'returned' evolved from the Old French word 'retourner', meaning 'to turn back'.

Initially, 'mistakenly' meant 'in error', and 'returned' meant 'to go back'. The combined form 'mistakenly-returned' retains the meaning of being sent back in error.