Douglas Harper's Etymology Dictionary
"not characteristic of American principles or methods, foreign to U.S. customs," 1818, from un- (1) "not" + American (adj.).\n\nEverything is un-American that tends either to government by a plutocracy or government by a mob.
[Theodore Roosevelt, 1917]
Wiktionary
a. 1 Contrary to the principles or institutions of United States. 2 Not good for interest of United States. 3 (context US spoken of another citizen English) unpatriotic; non-xenophobic. 4 (context informal English) incivil, immoral. alt. 1 Contrary to the principles or institutions of United States. 2 Not good for interest of United States. 3 (context US spoken of another citizen English) unpatriotic; non-xenophobic. 4 (context informal English) incivil, immoral.
WordNet
adj. considered contrary to the best interests of the United States
Wikipedia
Un-American is a pejorative term of U.S. political discourse which is applied to people or institutions in the United States seen as deviating from what are widely perceived to be fundamental American cultural and political values.
The most famous use is in the title of the House Un-American Activities Committee which was started to investigate alleged disloyalty and subversive activities on the part of private citizens, public employees, and those organizations suspected of having Communist ties. By 1959, former President Harry S. Truman had denounced the Committee as the "most un-American thing in the country today". The Committee lost considerable prestige as the 1960s progressed, and it was abolished by the House of Representatives in 1975.
The use and meaning of the term is by no means uniform in the US. Due in part to these historical associations with political abuses and jingoism, the attitudes of Americans toward the pejorative use of "Un-American" are often critical or suspicious. Moreover, Americans may vary widely in what they believe to be un-American.
Usage examples of "un-american".
So for the good of the environment, and the bank accounts of several well-placed individuals, private ownership of vehicles was labeled un-American, elitist, racist, wasteful, phallocentric, and just plain bad.
The prisoner database indicated only that Dunst was under investigation for possible un-American activities.
As I said to the reverend at one point, "I think boycotting is un-American.
A grand jury was in the works, an important grand jury that would have been as farreaching as the 1947 House Un-American Activities Committee hearings.
He practically insinuated that Milquetoast and his colleagues, by falling behind their deadlines, were guilty of un-American inactivity.
Given a choice—at least in my reading—I'm un-American enough to take quixotry over efficiency any day.
America gets suspicious because it's un-American not to make all the money you can, and sicks a Senior G-man on you, and now, by God, you're going to have to investigate yourself!
The superpatriotic chairman of the House Committee on Un-American Activities (HCUA), Rep.
It is a much more important issue than picketing the United Nations or parading in support of the House Un-American Activities Committee.
A member of the infamous Four Aces, she was committed to the Wittier Sanatorium by her husband, Henry van Renssaeler, shortly after her appearance before the House Committee on Un-American Activities.