flat-earther

[ flat-ur-ther ]
/ ˈflætˈɜr θər /

noun

a person who adheres to the idea that the earth is flat.
a person who clings to an idea or theory that has long been proved wrong.

Origin of flat-earther

1930–35; flat earth + -er1

British Dictionary definitions for flat-earther

flat-earther

noun

informal a person who does not accept or is out of touch with the realities of modern life