In English (which is the language being used here), American is the demonym for citizens of the US, while Canadian, Mexican, Argentinian, Peruvian, and Brazilia

In English (which is the language being used here), American is the demonym for citizens of the US, while Canadian, Mexican, Argentinian, Peruvian, and Brazilian are the typical demonyms of citizens of Canada, Mexico, Argentina, Peru, and Brazil. [0]: https://en.wikipedia.org/wiki/Demonym https://en.wikipedia.org/wiki/Demonym I'm aware that there are some continent categorizations that group North and South America as one continent called America, so one could use American to mean people who live in one of what are understood in other categorizations as North or South America. (Is that the continent categorization that you're familiar with? I just recently came across this, so if you wouldn't mind sharing where you learned this, and whether you're familiar with categorizations that count North America and South America separately, I'd be interested to hear more about it.) That doesn't, however, mean that the usage of American to mean citizen of the US is wrong: it's very widely used in English worldwide. USian is assuredly not widely agreed upon as an alternative, at least in English which is the language of discourse here. Words have multiple meanings that need to be understood in context. Sometimes that context needs to be clarified.