"Wingnut", wing nut or wing-nut, is a pejorative American political term referring to a person who holds extreme, and often irrational, political views. It is a reference to the extreme "wings" of a party, and shares a name with the hardware fastener also known as a wingnut.

According to Merriam-Webster, a "wingnut" is "a mentally deranged person" or "one who advocates extreme measures or changes: radical". Lexico, an online dictionary whose content comes from Oxford University Press, gives the political definition of "wing nut" as "A person with extreme, typically right-wing, views."

When William Safire – who was widely known as the "language maven" and wrote the "On Language" column for The New York Times Magazine from 1979 until 2009 – first wrote about "wing nut" in 2004, he said "In current political parlance ... the word is now beginning its bid to replace the tiring extremist. ... The true believers of each side consider those similarly inclined on the other to be nuts and kooks, a satisfying arrangement of derangement. ... The attack word catching on with political nonwingers and by mainstreaming media is wing nut. It is applied with supposed fine impartiality to both left-wing kooks and right-wing nuts", but by 2006, Safire would say "The prevailing put-down of right-wing bloggers is wingnuts; this has recently been countered by the vilification of left-wing partisans who use the Web as moonbats..." Later that year, Safire provided an example of the usage of "wingnut" in a Time magazine column by Joe Klein, in which Klein referred to "conservative wingnuts" (as opposed to "left-wing blognuts"), called Vice President Dick Cheney "the nation’s wingnut in chief", and said of the editorial page of The Wall Street Journal that it was "quasi-wingnut".

Two years later, in his book Safire's Political Dictionary, Safire was more definitive about the meaning and etymology of the word:

...[T]he political wingnut is an abbreviation of a longer term, in this case right-wing nut where nut, as slang for the head, has long been used to refer to a person who is silly, stupid, crazy, or simply nutty. ... The original right-wing nut is of considerable antiquity, dating at least to the 1960s...Today, the long and the short forms co-exist amicably in print.

David M. Herszenhorn of The New York Times has defined a "wing nut" as "a loud darling of cable television and talk radio whose remarks are outrageous but often serious enough not to be dismissed entirely," but he was careful to point out that the person he was so describing as a "wing nut" "...is the more notable because he hurls his nuts from the left in a winger world long associated with the right."

In his book Wingnuts: How the Lunatic Fringe is Hijacking America, author and columnist John Avlon defined a wingnut as "someone on the far-right wing or far-left wing of the political spectrum – the professional partisans, the unhinged activists and the paranoid conspiracy theorists. They're the people who always try to divide rather than unite us". Avlon also writes "I believe that the far left and the far right can be equally insane – but there's no question that in the first years of the Obama administration, the far right has been a lot crazier."

The examples Avlon gives of this "craziness" include the actions, beliefs and behaviors of those involved in the Oath Keepers, Posse Comitatus and other groups in the American militia movement, the Tea Party, "Obama derangement syndrome", the birth of "White-minority politics", the rise of right-wing media and the Republican echo chamber, Sarah Palin and the "Limbaugh brigades" of right-wing talk radio hosts, the Birther and Truther movements, and the GOP's "hyperconservative kamikaze caucus" in Congress. The only extended sections about "wingnuts" on the left deal with Keith Olbermann's news broadcasts, and the search by both sides for "heretics" within their respective parties, i.e. Republicans in Name Only and Democrats in Name Only (RINOs and DINOs).