diagonal

1 of 2

adjective

di·​ag·​o·​nal dī-ˈa-gə-nᵊl 

-ˈag-nəl

1

a

: joining two vertices of a rectilinear figure that are nonadjacent or two vertices of a polyhedral figure that are not in the same face

b

: passing through two nonadjacent edges of a polyhedron

a diagonal plane

2

a

: inclined obliquely from a reference line (such as the vertical)

wood with a diagonal grain

b

: having diagonal markings or parts

a diagonal weave

diagonal

2 of 2

noun

1

: a diagonal straight line or plane

2

a(1)

: a diagonal direction

(2)

: a diagonal row, arrangement, or pattern

b

: something oriented in diagonal position

3

: slash sense 4

see also:

on the diagonal

Synonyms of diagonal

Adjective

• oblique
• sloping
• leaning
• sloped

Noun

• slope
• inclination
• incline

Examples of diagonal in a Sentence

Adjective

The blanket is covered with diagonal stripes.

the diagonal design ran up the wall all the way from the lower left to the upper right-hand corner

Noun

a design with strong diagonals

the ramp was set at a low diagonal to make it easier for physically challenged patrons

Recent Examples on the Web

Adjective

The parallel groupings can be vertical, diagonal, horizontal, or a combination. — Madeline Buiano, Martha Stewart, 19 Sep. 2026

Beginning on her left side, the skirt boasted a waist-high, diagonal leg slit with a gauzy underlayer that showcased her peep-toe heels. — Chanel Vargas, InStyle, 18 Sep. 2026

Noun

Tzolis plays the pass and, because the Arsenal players are attacking the diagonal, there are a number of receivers available. — Jon MacKenzie, New York Times, 8 Sep. 2026

The most astonishing thing about this is that these numbers appear in the simplest contexts, such as when calculating the circumference of a circle or the diagonal of a square. — Manon Bischoff, Scientific American, 19 June 2026

Word History

Etymology

Adjective

Latin diagonalis, from Greek diagōnios from angle to angle, from dia- + gōnia angle; akin to Greek gony knee — more at knee entry 1

First Known Use

Adjective

1563, in the meaning defined at sense 1a

Noun

1571, in the meaning defined at sense 1

Phrases Containing diagonal

• diagonal matrix
• on a diagonal
• on the diagonal
• principal diagonal

Rhymes for diagonal

• hexagonal
• octagonal
• tetragonal

Kids Definition

diagonal

1 of 2 adjective

di·​ag·​o·​nal dī-ˈag-ən-ᵊl 

-ˈag-nəl

1

: joining two opposite corners of a four-sided figure

2

: running in a slanting direction

diagonally

-ən-ᵊl-ē, 

-nə-lē

adverb

diagonal

2 of 2 noun

1

: a diagonal line or direction

2

: a diagonal row, arrangement, or pattern

3

: slash entry 2 sense 2