# Main definitions of pentagon in US English:

: pentagon1Pentagon2

## pentagon1

### noun

• A plane figure with five straight sides and five angles.

• ‘They are marked by a pentagon with three overlapping triangles.’
• ‘Perfect crystal structures can contain pyramids, cubes, or hexagons, but not pentagons.’
• ‘Analysts also use a variety of symbols, such as parallelograms, pentagons, and others, to depict different types of events and activities.’
• ‘Although it is impossible to inscribe a regular pentagon in a square, an equilateral pentagon can be inscribed in two ways.’
• ‘When I looked at what she was doing, she was trying to work out (on the napkin) how to calculate the sum of the internal angles of a pentagon.’
• ‘In the second case, if the convex polygon is a pentagon incorporating all five points, then any four of these points can be connected to form a quadrilateral.’
• ‘They are formed from 60 atoms of carbon bonded together in a combination of pentagons and hexagons to form a ball, just like a soccer ball.’
• ‘For those who don't know, a buckyball is an extremely stable soccer-ball-shaped molecule made up of 20 hexagons and 12 pentagons.’
• ‘This says that the most stable arrangement is a pentagon surrounded by five hexagons.’
• ‘There are 24 ways to do it - make 12 pentagons, so that the mirror images are on each side of the pentagon.’
• ‘The balls are made with small pieces of wood 12 pentagons and 20 hexagons which fit together to form a sphere.’
• ‘Father entered the room, arms full of suitcases shaped in rectangles, pentagons, squares, and even spheres.’
• ‘Write the number 1 through 10 in the boxes below so each side of the pentagon has a sum of 14.’
• ‘Similarly, nine atoms can form a pentagon bonded to a hexagon, each ring sharing two atoms with the other ring.’
• ‘Of course, this statement has to be explained, since it is untrue if we understand distance in the usual way: the edges of these pentagons are visibly not straight and do not have the same length.’
• ‘In plan, the building is comprised of five concentric pentagons, known as rings.’
• ‘The hexagons, pentagons, and triangles that make up the biomes all have their own unique specification due to the irregular nature of the site.’
• ‘He calculates the side of a regular pentagon in terms of the radius of the circumscribed circle.’
• ‘Thus, you can readily obtain a curved pentagon, heptagon, and so on.’
• ‘You may know about a pentagon, a hexagon, or an octagon.’

### Origin

Late 16th century: via Latin from Greek pentagōnon, neuter (used as a noun) of pentagōnos ‘five-angled’.

## pentagon

/ˈpɛn(t)əˌɡɑn//ˈpen(t)əˌɡän/

## Main definitions of pentagon in US English:

: pentagon1Pentagon2

## Pentagon2

### proper noun

the Pentagon
• 1The pentagonal building serving as the headquarters of the US Department of Defense, near Washington, DC.

1. 1.1 The US Department of Defense.
‘the Pentagon said 19 of its soldiers had been killed’

## Pentagon

/ˈpen(t)əˌɡän//ˈpɛn(t)əˌɡɑn/