'illiberal' originates from Latin, specifically the word 'illiberalis', where the prefix 'in-' (rendered here as 'il-') meant 'not' and 'liberalis' meant 'of a free person; generous.'

'illiberal' changed from Late Latin 'illiberalis' into Middle English (via Old French influence such as 'illibéral' in some Romance forms) and eventually became the modern English word 'illiberal'.

Initially it meant 'not generous' or 'not of a free/civilized character', but over time its dominant sense shifted toward 'intolerant of liberal ideas' and opposition to liberal political or social freedoms.