'antirationalism' originates from combining the prefix 'anti-' and the noun 'rationalism'; 'anti-' comes from Greek 'antí' meaning 'against', and 'rationalism' comes from Latin 'rationalis' (from 'ratio') meaning 'reason'.

'rationalism' changed from Latin 'rationalis' (relating to reason) through Medieval Latin and Old/Middle French into the English word 'rationalism'; the full compound 'antirationalism' was formed in modern English by prefixing 'anti-' to 'rationalism'.

Initially it meant 'opposition to rationalism'; over time the term has been used more broadly to describe attitudes, movements, or philosophies that devalue reason in favor of faith, tradition, emotion, or intuition.