Un-American is a term of US political discourse which is sometimes applied to people or institutions in the United States in an attempt to deny the targets the identity of American. It implies a substantial deviation from US norms and may extend to internal subversion, espionage or treason.
The most famous use is in the title of the House Un-American Activities Committee which was started to combat Nazi and Ku Klux Klan (KKK) activity in the US during World War II and which later investigated the activities of Communists and purported Communists in the US. By 1959, however, former President Harry S. Truman had denounced the House Un-American Activities Committee as the "most un-American thing in the country today."
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.
Additionally, liberals and progressives have described as un-American recent federal legislation in the U.S. that they view as an attack on civil liberties. The term (or similar sentiments) has been used by political supporters in the media to describe actions or beliefs that are critical of their candidate's policies..
The term "un-American" may be used in ad hominem attacks, meant to quash the arguments of American opponents by depicting them as subversive, unpatriotic or deviant. As a result, it is often used in a satirical or sarcastic manner; similarly, its frequent appearance in situations that do not merit its use has further diluted its original, pre-McCarthyism meaning. As it is so frequently applied in a hyperbolic manner, and as it has its origins in American political responses to the ideologies of the Ku Klux Klan and the Nazi Party under Hitler, the debate-ending and perhaps amusing appearance of the term "un-American" is similar to Godwin's Law and reductio ad Nazium.
In Canada the word "un-Canadian" is sometimes used, generally with the implication that a political official or organisation is doing something improper by the lights of Canadian values (e.g., contrary to the principle of peace, order, and good government), particularly towards Quebec sovereignists.
Another analogous usage is reflected in the Chinese use of the term "un-Chinese" to refer to people who violate norms of "canonical" Chinese culture or who are otherwise refused the identity of Chineseness by some Chinese.