Noun
(US, colloquial) Someone who tells the truth. [from 20th c.]
(colloquial, chiefly US) Someone who believes that the US government was responsible for the 9/11 attacks. [from 21st c.]
(by extension) A conspiracy theorist who does not believe the accepted story about some significant event, fact, etc. [from 21st c.]
Source: en.wiktionary.org