'invalid' originates from Latin, specifically the word 'invalidus,' where 'in-' meant 'not' and 'validus' meant 'strong.'

'invalidus' transformed into the Old French word 'invalide,' and eventually became the modern English word 'invalid' through Middle English.

Initially, it meant 'not strong,' but over time it evolved into its current meanings of 'not valid' and 'a person made weak by illness.'