'antichristianity' originates in English, formed from the prefix 'anti-' (from Greek 'anti-' meaning 'against') + 'Christianity' (from Greek/Latin 'Christianus/Christianos' referring to followers of Christ).

'Christianity' comes from Greek 'Christianos' (followers of 'Christos' meaning 'anointed'), passed into Latin as 'Christianus' and Middle English as 'Christianity'; the prefix 'anti-' (Greek 'anti-') has been attached in English to form compounds expressing opposition, producing 'antichristianity'.

Initially the components meant 'against' + 'followers of the anointed one'; over time the compound has been used to mean general opposition to Christian beliefs or institutions ('opposition to Christianity').