Pentagon

(pěnta-gon.) (From Gr. pente, five, and go nia, an angle.) (Geom.) A plane figure having five sides and five angles. If the five sides are equal, it is called a regular P. Its area is equal to five times the sine of 36° multiplied by the cosine of the same; and the square of the side of a regular P. is equal to the sum of the squares of the sides of the hexagon and decagon inscribed in the same circle.- (Fort.) A fort with five bastions. Pentahedron, (-e'dron.) [FromGr. pente, and hed ra, abase.] (Geom.) A solid figure having five equal sides or faces. [s. 696]