'illiberalism' originates from English, formed by the adjective 'illiberal' + the suffix '-ism', where 'illiberal' uses the negative prefix 'il-' (from Latin 'in-' before 'l-') + 'liberal' (from Latin 'liberalis' meaning 'of freedom, generous').

'liberalis' in Latin gave rise to Old/French forms like 'liberal' and then Middle/Modern English 'liberal'; English formed 'illiberal' by adding the negative prefix 'il-' to 'liberal', and the noun 'illiberalism' was formed by adding the productive noun-forming suffix '-ism' to describe the doctrine or tendency.

Originally related to 'liberalis' meaning 'of freedom' or 'generous', the compound 'illiberalism' later came to mean the opposition to those liberal values — i.e., restriction of freedoms and rejection of liberal democratic norms.