'antitax' originates from Modern English, specifically formed by combining the prefix 'anti-' (from Greek 'anti-' meaning 'against') with the word 'tax' (from Latin 'taxare' via Old French 'taxer'), where 'anti-' meant 'against' and 'tax' meant 'assessment or levy'.

'tax' comes from Latin 'taxare' (to estimate, assess), passed into Old French as 'taxer' and into Middle English as 'tax'; the compound 'anti-' + 'tax' produced the modern English formation 'antitax' (often written 'anti-tax' or 'anti tax' in earlier usage).

Initially the elements meant 'against' + 'assessment/levy'; over time the compound came to mean specifically someone or something opposing taxes or tax policy.