'immunocompetent' originates from the combination of 'immune' and 'competent', where 'immune' refers to the body's ability to resist harmful microorganisms and 'competent' means having the necessary ability or skills.

'immune' and 'competent' were combined in the 20th century to form 'immunocompetent', reflecting the concept of a fully functioning immune system.

Initially, it meant 'having the ability to resist disease', and this meaning has largely remained the same in modern usage.