A pentagon is a flat shape with five straight sides and five angles. In the United States, “the Pentagon” also refers to the five-sided building that is the headquarters of the Department of Defense.
“Pentagon” comes from Greek *pente* (“five”) and *gōnia* (“angle”). It literally means “five-angled.”
Once you know *pente* is five and *gon* is angle, words like pentagon, hexagon, and octagon suddenly make sense as a family. The famous U.S. Pentagon is literally named after its math shape. It’s one of the rare times geometry turns into a global political symbol.
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