Origin: Greek suffix -gon
Pentagon has 5 different meanings across 2 categories:
a government building with five sides that serves as the headquarters of the United States Department of Defense
"The president addressed the nation from the historic pentagon, which stands as the central command post for the U.S. military."
the United States military establishment
"The Pentagon announced new budget cuts that will affect every branch of the armed forces."
a five-sided polygon
"The architect sketched a simple pentagon on the napkin to illustrate the basic shape of the building's footprint."
A polygon with five sides and five angles.
"The regular pentagon drawn on graph paper has exactly five equal sides and five interior angles."
In plain English: A pentagon is any shape that has five sides and five corners.
"The US government is located in a large building shaped like a pentagon near Washington DC."
Usage: The term refers to any geometric shape with exactly five straight sides, though it is most commonly used as the proper noun for the United States Department of Defense headquarters building in Washington, D.C. Do not confuse this specific government complex with generic five-sided figures unless discussing geometry or architecture specifically.
The headquarters of the United States of America's Department of Defense.
"The President gave a press briefing at the Pentagon to announce new military strategies."
The word pentagon comes from Ancient Greek and originally described a shape with five angles. It traveled into English through Middle French and Late Latin before taking on its modern geometric meaning.