'immunoincompetent' originates from Modern English, formed by combining the combining form 'immuno-' (from New Latin 'immunis', ultimately Latin, meaning 'exempt' or 'protected') and the adjective 'incompetent' (from Latin 'incompetentem', from 'in-' 'not' + 'competentem' 'suitable/able').

'immunoincompetent' was coined in 20th-century medical English by compounding 'immuno-' (relating to immunity) with 'incompetent' (entered English via Latin/Old French roots); the components 'immuno-' and 'incompetent' themselves derive from Latin roots and merged into a specialized clinical term.

Initially, 'immuno-' in historical usage related to being 'exempt' and 'incompetent' meant 'not suitable' or 'lacking ability'; over time these elements came to mean 'relating to immunity' and 'lacking functional ability' respectively, yielding the modern combined meaning 'lacking immune competence'.