pentagon

pentagon — noun

1. a closed shape made from five straight lines, creating five points

1.nounB2
Definition

a closed shape made from five straight lines, creating five points

Example

Nina drew a pentagon on the poster with a black marker.

draw a pentagon

The map showed a pentagon beside the square and the triangle.

Common collocations
  • regular pentagon
  • draw a pentagon
  • pentagon shape
  • pentagon corners
Synonyms
  • polygon

    the general class word; a pentagon is one kind of polygon

  • five-sided figure

    clear descriptive wording, but less standard than the math term

  • shape

    much broader and not limited to figures with straight sides

Antonyms
  • triangle

    has three sides instead of five

  • hexagon

    has six sides instead of five

Grammar Patterns

draw a pentagon

a regular pentagon

a pentagon with five corners

Usage Note

Usually countable in math and design. Common with words that show shape or drawing, such as regular, draw, corner, and side.

Common Mistakes

A pentagon has six sides.
A pentagon has five sides.
the word always refers to a five-sided figure.

2. the large five-sided headquarters near Washington, D.C., and also the American d

2.nounB2
Definition

the large five-sided headquarters near Washington, D.C., and also the American defense department it stands for in news reports

Example

Reporters waited outside the Pentagon before the news meeting started.

literal place: outside the Pentagon

The Pentagon announced new aid after the storm hit the island.

metonymic use: the department announced something

Common collocations
  • Pentagon officials
  • Pentagon report
  • Pentagon meeting
  • outside the Pentagon
Synonyms

Grammar Patterns

the Pentagon announced...

outside the Pentagon

inside the Pentagon

Usage Note

Usually capitalised and used with the. In news writing, it often names the defense department or its leaders, not only the building.

Common Mistakes

pentagon said the plan was ready.
The Pentagon said the plan was ready.
this proper noun normally takes a capital P and the article 'the'.

Word family

  • pentagonal
    adjectiveC1

Synonym discussion

Sense: noun/1

For the geometric sense, pentagon is more exact than polygon. Polygon is the broad class word for any flat shape with straight sides, so a pentagon is one member of that group. Triangle and hexagon are useful contrasts because they name shapes with three and six sides. Five-sided figure explains the meaning clearly, but it sounds more descriptive and less like the standard word used in math lessons. Use pentagon when the exact number of sides matters: 'The badge is a pentagon, not a circle.' A teacher might first use the broad term and then narrow it: 'Today we will draw a regular pentagon.'

pentagon ↗polygontriangle ↗hexagonfive-sided figure

Etymology

GreekLatinFrenchEnglish

Pentagon comes from old Greek parts meaning 'five' and 'angle'. The word passed through Latin and French before entering English as the name of a five-cornered figure. Much later, it also became the familiar name of the famous five-sided U.S. defense headquarters.