Flat
Flat adjective - Being neither more nor less than a certain amount, number, or extent.
Mountainous is an antonym for flat.
Mountainous
Mountainous adjective - Unusually large.
Flat is an antonym for mountainous.
Nearby Words: mountain, mountaineer
Both words in one sentence
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Upon arriving at the site, Penn decided it did not look the way Alaska should look (it was flat with marshy grasslands), and decided to film in another location in Alaska that was more mountainous and conformed to the Hollywood ideal of what Alaska was supposed to look like.
Source: Film / Into the Wild -
The world is "mostly flat with some hilly and mountainous areas" but the cities themselves feature solid houses and walls that are climbable and the dungeons just revel in the fact that you can cross over your own path on three or four different levels.
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The transition between the northernmost regions of Spain and the rest of the country is somewhat dramatic, when you go from the endless, almost flat, and with few trees Spain's plateau to the lush and mountainous Green Spain as is known after crossing the Cantabrian mountains.
Source: Patchwork Map
Cite this Source
Mountainous and Flat. (2016). Retrieved 2026, August 14, from https://thesaurus.plus/related/flat/mountainous
Flat & Mountainous. N.p., 2016. Web. 14 Aug. 2026. <https://thesaurus.plus/related/flat/mountainous>.
Mountainous or Flat. 2016. Accessed August 14, 2026. https://thesaurus.plus/related/flat/mountainous.
Google Ngram Viewer shows how "flat" and "mountainous" have occurred on timeline