'pro-atheism' originates from Modern English, combining the prefix 'pro-' (from Latin 'pro', meaning 'for' or 'in favor of') and 'atheism' (from Greek roots), where 'pro-' meant 'in favor of' and 'atheism' meant 'absence of belief in gods'.

'atheism' comes from Greek 'atheos' (a- 'without' + theos 'god'), passed into Latin and then into Middle and Modern English as 'atheism'; 'pro-' derives directly from Latin 'pro' meaning 'for', and the compound 'pro-atheism' developed in Modern English by joining these elements.

Initially the parts meant 'for' + 'without god(s)', and the compound has retained the meaning of 'being in favor of atheism' though contemporary usage can range from neutral support to activist promotion.