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1.
a resident of the United States
(Pronounced you-ess-ee-yen)
Tom is a USian, that yank.

Benji is a Non-USian, that Tommy.
by Forkman August 21, 2008
 
2.
A demonym, used especially in internet based writing, used to indicate that someone or something is of the United States of America. This is contrasted with "American," which technically means someone or something belonging to North or South America, including such disparate places as Guyana, Mexico, and Canada.
Damaris, Ashley, and Yulisa are all Americans, but only Damaris is USian.
by ProudUSian March 15, 2011
 
3.
1. Of or pertaining to the United States of America

2. A Citizen of the United States of America

A sometimes pejorative term coined in recent years on various internet discussion boards. Meant to resolve the ambiguous nature of the terms "North American," which could be taken to refer to Canada or the United States, and "American," which could be taken to refer to North America, South America, or the United States.
1. I'm not a fan of all of this USian war-mongering.

2. You'd never understand universal healthcare--you're a USian.
by Lucian March 15, 2005
 
4.
Irritating neologism used by internet commentators who lack an ability to comprehend context. Primarily an indicator of autism.
"I don't understand why USians insist on calling themselves Americans."
by docAmerica May 21, 2009
 
5.
Derogatory term used to refer to citizens of the United States of America. Usually used by those who want to insult the USA or American citizens while loudly proclaiming they are simply trying to differentiate between citizens of the USA and citizens of other nations in the North and South American continents.
You are just like every other USian , arrogant and egotistical, not like other Americans.
by Forrest Horn, Sr. April 27, 2006
 
6.
A racial slur used by Central and some South Americans to demean real Americans.
Well we might not have freedom or democracy like the USians but at least we Venezuelans have cheap oil.
by ChigacoDCJ August 09, 2009