Also found in: Idioms, Wikipedia.


One who stubbornly adheres to outmoded or discredited ideas.

[From the long-discredited belief that the earth is flat.]

flat′-earth′ adj.
American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.


informal a person who does not accept or is out of touch with the realities of modern life
Collins English Dictionary – Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014
References in periodicals archive ?
Any other position renders its holder a "flat-earther."
Some officials might fear that not removing hate speech or offensive comments could be viewed as implicit endorsement of those messages, but few would accuse NASA of promoting conspiracy theories for not removing flat-Earther comments on Instagram.
The rejection of established truths and the expertise that allowed these truths to become knowable is maybe not so dangerous in the hands of a random, garden-variety flat-earther, but much more dangerous in the hands of, say, Donald Trump, who is not a scientist or an expert in any conceivable way, but who can convince an unintelligent populace that climate change isn't real.
In the following video, watched by over 24 million on the planet - flat or spherical - a determined Flat-Earther explains their theory in detail:
INTERNATIONAL space agency NASA has responded to the flat-Earther heading for North Wales with a simple message - the Earth is "not flat".
They kick off Magic Weekend against Toulouse in Newcastle on Saturday, another platform to showcase a dynamic brand that must have the flat-earther traditionalists choking on their chips.
Flat-earther Peter Versoza, Vintendo, James "Lodi" Martinez, Alexander Belmonte III, and Revo Ranger will attempt to put an end to Sinnsyk's reign as they engage in the largest All Out War match in PWR history.
An ambiguous Facebook post by a Pakistani round/oval-earther was tackled brilliantly by an Indian flat-earther.
And please Mr Bennett, do lay off insults like "flat-earther", they're only used by those with no evidence to offer, as I'm sure most people appreciate.
Even the most stubborn flat-earther now has to concede that timing different stages of a race tells us how its development has favoured some and worked against others.
I am far from being a 'flat-earther' who believes mankind has done no damage to the global climate condition; nor do I necessarily believe that nature will, without our help, be able to--at best--repair, or--at worst--adjust to the prevailing conditions.
It worries me that instead of having a sensible conversation on just how much man is responsible for changing the climate, anyone who doesn't toe the man-the-planet-destroyer line is now barracked as a fool and a flat-Earther.