'non-Americanly' originates from English, specifically formed from the negative prefix 'non-' + 'American' + the adverbial suffix '-ly'. 'non-' ultimately comes from Old English/Proto-Germanic (Old English elements such as 'nān'/'ne') where it meant 'not'; 'American' derives from 'America' (named after the Italian explorer Amerigo Vespucci); '-ly' is an English suffix used to form adverbs.

'non-Americanly' developed by attaching the adverbial suffix '-ly' to the compound 'non-American' (from 'non-' + 'American'). 'American' itself entered English via modern Latin/Italian usage of the place-name 'America' in the early modern period, named after Amerigo Vespucci; the full adverbial form is a straightforward modern English formation.

Initially the parts signified 'not' + '(of) America' + 'in the manner of' and the combined form retained that literal sense; over time it has been used idiomatically to mean 'in a manner not characteristic of American culture or style.'