Names for United States citizens

Different languages use different terms for citizens of the United States, who are known in English as "Americans." All forms of English refer to U.S. citizens as "Americans," a term deriving from "America"; in the English context, it came to refer to inhabitants of British North America, and then the United States. However, there is some linguistic ambiguity over this use due to the other senses of the word "American," which can also refer to people from the Americas in general. Other languages, including French, German, Japanese, and Russian, use cognates of "American" to refer to people from the United States, while others, particularly Spanish, primarily use terms derived from "United States." There are various other local and colloquial names for Americans.

Amerigo Vespucci first demonstrated that Brazil and the West Indies did not represent Asia's eastern outskirts as conjectured by Christopher Columbus, but instead constituted an entirely separate landmass hitherto unknown to the peoples of the Old World. Martin Waldseemüller coined the term “America” (in honor of Vespucci) in a 1507 world map.

First uses of the adjective "American" referenced European settlements in the New World. "Americans" referred to the indigenous peoples of the Americas, and subsequently to European settlers and their descendants. English use of the term "American" for people of European descent dates to the 17th century; the earliest recorded appearance is in Thomas Gage's The English-American: A New Survey of the West Indies in 1648. In English, "American" came to be applied especially to people in British America, and thus its use as a demonym for the United States derives by extension.

...
Wikipedia