Noun, adjective. The national name for the citizens of the United States of America. Not American, which means from America, the continent
Luca: Ezekiel, what think you about the United Statesian Occupation in Iraq?
Ezekiel: Mmmm... easy to say. A big split-up by an avaricious and selfish man, thus, George W. Bush.
Ezekiel: Have you heard of the party at Fatima's house?
Luca: No... was there one?
Ezekiel: Yes! it was full of United Statesians, Canadians and Brazilians.
An incorrect term applied to citizens of the United States of America generally out of anger that they would presume to call themselves Americans. The politically correct term would be United States Citizen. The proliferation of the term American (often by members of other North and South American nations) to refer to such people has made it appropriate to do so.
I hate those presumptuous united statesians.