'readjustment' originates from Latin prefix 're-' (meaning 'again') combined with the English verb 'adjust', which in turn comes from Old French 'ajuster' (ultimately from Latin 'justus', where the root 'just-' meant 'right' or 'proper'), plus the nominalizing suffix '-ment'.

'adjust' changed from Old French 'ajuster' (via Middle English forms such as 'adjusten') and became modern English 'adjust'; later English formed 'readjust' by adding prefix 're-' and then the noun 'readjustment' by adding suffix '-ment'.

Initially, the root idea was 'to make right or proper' (from Latin 'justus'); over time the sense broadened to 'to set or change to fit' and 'readjustment' came to mean 'adjusting again' or 're-adapting' in both physical and psychological senses.