'unjustly-gained' originates from the combination of 'unjustly' and 'gained', where 'unjustly' is derived from 'unjust', meaning 'not just', and 'gained' from 'gain', meaning 'to obtain'.

'unjustly' evolved from the Old French word 'injuste', and 'gained' from the Old English 'gægn', eventually forming the modern English term 'unjustly-gained'.

Initially, 'unjustly' meant 'not fair', and 'gained' meant 'obtained'. Together, they have retained the meaning of 'obtained in an unfair manner'.