'tax-opposed' originates from modern English as a compound of 'tax' and 'opposed'. 'tax' in turn originates from Latin, specifically the word 'taxare', where 'tax-' meant 'to assess'; 'opposed' originates from Latin, specifically the word 'opponere', where 'ob-' (or 'op-') meant 'against' and 'ponere' meant 'to place'.

'tax' passed into Old French ('taxer') and Middle English before becoming the modern English 'tax'; 'opponere' passed into Old French as 'opposer' and Middle English as 'oppose(d)', and the compound 'tax-opposed' formed in modern English by combining these elements.

Initially, the components meant 'to assess' (for 'tax') and 'to place against' (for 'opposed'); over time the combined compound came to mean 'being against taxation' in modern usage.