heptagon

n. seven sided polygon

In geometry, a heptagon is a polygon with seven sides and seven angles. In a regular heptagon, in which all sides and all angles are equal, the sides meet at an angle of 5π/7 radians, 128.5714286 degrees. Its Schläfli symbol is {7}. The area of a regular heptagon of side length a is given byThe heptagon is also sometimes referred to as the septagon, using "sept-" (an elision of , a Latin-derived numerical prefix, rather than , a Greek-derived numerical prefix). The OED lists "septagon" as meaning "heptagonal".
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Noun
1. a seven-sided polygon
(hypernym) polygon, polygonal shape

(n.)
A plane figure consisting of seven sides and having seven angles.
  

geol. heptagon