'ex-serviceman' is formed from the prefix 'ex-' (Latin 'ex' meaning 'out of' or 'former') combined with 'serviceman' (from 'service' + 'man').

'service' comes via Old French 'service' from Latin 'servitium' (related to 'servire', 'to serve'); 'man' comes from Old English 'mann'. The compound 'serviceman' developed in Modern English to mean a person serving (especially in armed forces), and the prefix 'ex-' was later added to indicate former status.

Originally, 'serviceman' referred to a person in service; over time it came to be used particularly for those serving in the armed forces. 'Ex-serviceman' therefore evolved to mean someone who has formerly served in the military.