'heterodoxly' originates from English, specifically from the adjective 'heterodox' plus the adverbial suffix '-ly'. 'heterodox' ultimately comes from Greek 'heterodoxos', where 'hetero-' meant 'different' and 'doxa' meant 'opinion'.

'heterodox' passed from Greek 'heterodoxos' into Medieval/Modern Latin and then into English as 'heterodox'; the adverb 'heterodoxly' was formed in English by adding '-ly' to the adjective.

Initially it meant 'holding a different opinion'; over time it has come to mean 'not conforming to established or orthodox beliefs or practices' in modern usage.