A person who lives at low altitude - used by those living at higher altitudes(noun)
An inhabitant of or observer in a universe with two spatial dimensions.(noun)
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Use "flatlander" in a sentence
"I grew up as something native Vermonters refer to as a flatlander, a person from New York or New Jersey who visits the state to ski, to hike, to watch the leaves turn in the fall."
"Everywhere in human space a flatlander is a schnook who never gets above the atmosphere."
"A lifelong actor and performer, Lorber — a Democrat — got into politics in 2005 when he ran for and won election to a House seat in Burlington, despite being a "flatlander" — or non-native Vermonter."