It's the word or similar to the word for the USA in a few languages, like Esperanto ("Usono": the USA, "Usonano": a USA citizen, "Ameriko" already being used for the continent and "Amerikano" for people from that continent). It was a term introduced in the 1800s without a lot of success, then after its use in Esperanto it was mildly popularised by American architectural legend Frank Lloyd Wright, who embraced the term and described his work as "Usonian architecture" and wrote at length about "Usonian character."