'anti-radicalist' originates from a combination of 'anti-' from Greek 'antí-' meaning 'against' and 'radicalist', formed from 'radical' (from Latin 'radicalis' from 'radix' meaning 'root') plus the agentive suffix '-ist' (from Greek/Latin) meaning 'one who'.

'radical' entered English via French and Latin (from Latin 'radicalis' from 'radix' meaning 'root'); the compound 'anti-radical' and the agentive form 'anti-radicalist' developed in modern English (19th–20th century) to describe people opposing radical political movements.

Initially it simply meant 'against radicals' or 'opposed to radicalism'; over time it has come to denote more specifically a person or group resisting radical political or social change.