'anti-Americanly' originates from a combination of elements in English: the prefix 'anti-' (from Greek 'anti' meaning 'against'), the proper noun 'America' (named after the Italian explorer 'Amerigo Vespucci'), and the adverbial suffix '-ly' (from Old English '-līc' meaning 'like' or 'in the manner of').

'anti-Americanly' developed by adding the Greek-derived prefix 'anti-' to 'American' to form the adjective 'anti-American', and then adding the Old English-derived adverbial suffix '-ly' (from '-līc') to create the modern adverb.

Initially the element 'anti-American' meant 'opposed to America' (descriptive adjective); with the addition of '-ly' it evolved into an adverb meaning 'in an anti-American manner'.