diagonal

American  

[dahy-ag-uh-nl, -ag-nl] / daɪˈæg ə nl, -ˈæg nl /

adjective

1. Mathematics.

   1. connecting two nonadjacent angles or vertices of a polygon or polyhedron, as a straight line.

   2. extending from one edge of a solid figure to an opposite edge, as a plane.

2. having an oblique direction.

3. having oblique lines, ridges, markings, etc.

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noun

1. a diagonal line or plane.

2. virgule.

3. a diagonal row, part, pattern, etc.

4. Manège. (of a horse at a trot) the foreleg and the hind leg, diagonally opposite, which move forward simultaneously.

5. diagonal cloth.

6. Mathematics. a set of entries in a square matrix running either from upper left to lower right main diagonal, or principal diagonal or lower left to upper right secondary diagonal.

7. Chess. one of the oblique lines of squares on a chessboard.

   He advanced his bishop along the open diagonal.

diagonal British  

/ daɪˈæɡənəl /

adjective

1. maths connecting any two vertices that in a polygon are not adjacent and in a polyhedron are not in the same face

2. slanting; oblique

3. marked with slanting lines or patterns

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noun

1. maths a diagonal line or plane

2. chess any oblique row of squares of the same colour

3. cloth marked or woven with slanting lines or patterns

4. something put, set, or drawn obliquely

5. another name for solidus

6. one front leg and the hind leg on the opposite side of a horse, which are on the ground together when the horse is trotting

diagonal Scientific  

/ dī-ăg′ə-nəl /

1. Connecting two nonadjacent corners in a polygon or two nonadjacent corners in a polyhedron that do not lie in the same face.

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1. A diagonal line segment.

Other Word Forms

• diagonally adverb
• nondiagonal adjective
• nondiagonally adverb

Etymology

Origin of diagonal

First recorded in 1535–45; from Latin diagōnālis, from Greek diagṓn(ios) “from angle to angle” + Latin -ālis adjective suffix; dia-, -gon, -al ¹

Explanation

A diagonal is made out of a straight line that's set at an angle instead of straight up or across. If you picture a square and draw a line connecting the opposite corners, that’s a diagonal line. You’ll find diagonal lines in geometry, and also in the world around you. A quarterback might throw a diagonal pass that angles across the field, or you might buy a snazzy new leotard with diagonal stripes. Diagonal can be either a noun or an adjective. You could call the steep slope of a hill a diagonal across the sky, or you could talk about the diagonal hillside reaching up toward the clouds.

Example Sentences

"But, in the Sagittarius Arm, it's going counterclockwise. We didn't understand how the transition occurred. Then one day, Anna brought in some data, and I went, 'O.M.G., the reversal's diagonal!'"

From Science Daily • Feb. 24, 2026

Known as the Klaebo stride, or Klæbo-klyvet in Norwegian, it’s a running style used on steep uphills where he essentially sprints on his skis, leaving competitors who use traditional diagonal striding behind.

From The Wall Street Journal • Feb. 10, 2026

She was holding a cup of coffee and a homemade turkey sandwich — white bread, cut on the diagonal, slathered with Kewpie mayo and layered with lettuce — tucked into a brown paper bag.

From Salon • Jan. 19, 2026

In terms of long passing, Virgil van Dijk possesses a great long diagonal pass that has found Mohamed Salah isolated on the right wing numerous times over the last few years to similar effect.

From BBC • Oct. 19, 2025

Struts and diagonal rods ran between the two wheels to stiffen the assembly and give it the strength of a railroad bridge.

From "The Devil in the White City" by Erik Larson

Related Words

• crosswise
• oblique
• slanted