'immunodeficiency' originates from Latin, specifically the word 'immunis,' where 'immun-' meant 'exempt' and 'deficientia' meant 'failing or lacking.'

'immunis' transformed into the French word 'immunité,' and eventually became the modern English word 'immunity,' with 'deficientia' contributing to the term 'deficiency.'

Initially, it meant 'lacking immunity,' and this meaning has largely remained the same in modern usage.