truther

The story

From truth + -er (occupational suffix) or + -er (“supporter”). For sense 2, directly from name of the 9/11 Truth movement.

First known use, by meaning

• from 20th c. Someone who tells the truth.
• from 21st c. Someone who believes that the US government was responsible for the 9/11 attacks.
• from 21st c. A conspiracy theorist who does not believe the accepted story about some significant event, fact, etc.