From Longman Dictionary of Contemporary Englishpentagonpentagon noun [countable] CFa flat shape with five sides and five angles —pentagonal /penˈtæɡənəl/ adjectiveExamples from the Corpus

pentagon• It is easy to see that there are 12 pentagons on the ball.• They are completely regular solids: each has all of its faces repeating a regular polygon, triangle, square or pentagon.• Two methods for construction of the regular pentagon.• The regular pentagon, in association with the hexagon, has been credited with magical powers throughout recorded history.• A group of six pentagons folds naturally to form a serrated hemisphere.• Folding of square, pentagon, ellipse, spider and tetrahedron.• All the magic of the pentagon is transferred to this solid.• For example, the square has four-fold symmetry, the pentagon has five-fold, the hexagon has six-fold symmetry.