'ex-soldier' originates from the prefix 'ex-' meaning 'former' and the word 'soldier' from Old French 'soudier', which meant 'one who serves in an army'.

'soudier' transformed into the Middle English word 'souldier', and eventually became the modern English word 'soldier'.

Initially, it meant 'one who serves in an army', but over time it evolved to include those who have served in the past, hence 'ex-soldier'.