americanise has 1 distinct synonym spread across 2 of its 2 senses. Each sense below keeps its own list, because a synonym belongs to a meaning and not to a word: swapping one sense's substitute into another sense's sentence is how a thesaurus makes writing worse. WordNet records no antonym for it — antonymy is a relation between word forms rather than concepts, so it is deliberately sparse.
Counts are distinct word forms across every sense. A synonym that appears under three senses is counted once here and shown three times below, under each sense it belongs to.
make American in character
“The year in the US has completely Americanized him”
become American in character
“After a year in Iowa, he has totally Americanized”
Synonyms, antonyms and the broader and narrower relations for americanise come from Princeton University’s WordNet. Full sources and licences.