truther

noun

1. (US, colloquial)Someone who tells the truth.

   “A liar can't begin to start the riots a truther can.”

2. (US, colloquial)Someone who believes that the US government was responsible for the 9/11 attacks.

   “[signed] 9/11 Truther”

   “Therefore, virtually every press release or statement about 9/11 should include a reference to the poll to show people that many Americans are 9/11 truthers who scoff at the 9/11 Commission as a fraud and that demand a real 9/11 investigation.”

   “The Iranian president is even a "truther," insisting that there was a hidden hand behind Sept. 11, 2001. "Could it be planned and executed without coordination with intelligence and security services — or their extensive infiltration?" he mused in the letter to Bush.”

3. (broadly)A conspiracy theorist who does not believe the accepted story about some significant event, fact, etc.

   “For instance, "truthers" who believe in a US government conspiracy to destroy the pentagon”

   “Rather, believers of this conspiracy theory (known as Sandy Hook “truthers”) propose that the entire event might have been staged by Homeland Security and FEMA”

   “I am calling your attention to it because I think that we JFK truthers may be able to use this film to our advantage.”

4. (humorous, slang)An advocate, especially for a headcanon.