Someone who not only believes the Earth is flat, but will also claim any argument against their theory is government propaganda.

a person who does not accept or is out of touch with the realities/ beliefs of modern times;

one who blatantly dismisses/ disagrees with common knowledge or scientific findings.

Being a Flat Earther is a lifelong developmental disability that affects how people perceive the world and interact with others. Flat Earther people can have difficulties with everyday social communication, social interaction, repetitive behaviours and sensory issues

A person who believes that the earth is flat.

A separate line of the genus homo sapiens (Humans) who believe that earth is flat. They lack in comprehension and learning skills seeing they believe earth is flat which is of course WRONG.

A Flat Earther is a person who pursues the belief that the world is flat, and tries to discredit centuries of astronomical discovery and scientific advancement, based on a childlike limited understanding of science and religion. No amount of proof or evidence will convince a Flat Earther that the earth is round like a ball, because their brain lacks the capacity to understand this reality.

In Indonesia, also used for people from Islam-related organizations (FPI, FUI, PKS) and their followers that is too easy to be fooled, too easy to believe their preacher/ulama. Even though what they say and do violated Islam rules, like rejecting to pray for dead body just because he/she voted for that religion blasphemy accused governor (Ahok) when alive.

In Indonesian, said as "kaum bumi datar". This term also comes from flat earth concept. Their preacher used to talk about flat earth in mosques over and over again before Jakarta governor vote campaign started.