Flat
Flat adjective - Being neither more nor less than a certain amount, number, or extent.
Perpendicular
Perpendicular adjective - Rising straight up.
Usage example: river rafters staring awestruck at the canyon's nearly perpendicular cliffs
Flat is an antonym for perpendicular.
Nearby Words: perpendicularity, perpendicularly
Both words in one sentence
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The issue is that a 90-degree angle only looks like two perpendicular lines intersecting at a point on a flat two-dimensional plane.
Source: Alien Geometries - While the game Cortex Command is a side-scroller which takes place mostly on the ground, in the opening cinematic it shows a flat view of a planet, and orbiting the planet exactly perpendicular to our view, is a Trade Star.
Source: 2-D Space
Cite this Source
Perpendicular and Flat. (2016). Retrieved 2026, July 21, from https://thesaurus.plus/related/flat/perpendicular
Flat & Perpendicular. N.p., 2016. Web. 21 Jul. 2026. <https://thesaurus.plus/related/flat/perpendicular>.
Perpendicular or Flat. 2016. Accessed July 21, 2026. https://thesaurus.plus/related/flat/perpendicular.
Google Ngram Viewer shows how "flat" and "perpendicular" have occurred on timeline