'antireligiousness' originates from English formation combining the prefix 'anti-' (from Greek 'antí', meaning 'against') with 'religious' (from Latin 'religiosus', from 'religio', meaning 'religion' or 'reverence'), plus the noun-forming suffix '-ness'.

'religious' entered English via Old French/Latin: Latin 'religiosus' (from 'religio') passed into Old French and Middle English as 'religious', while the prefix 'anti-' comes from Greek 'antí'. These elements were combined in modern English to form 'antireligious' and then 'antireligiousness'.

The element 'anti-' originally meant 'against' and, combined with 'religious', formed a term that has meant 'opposed to religion' since its formation; the overall meaning (the state of opposition to religion) has remained stable.