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.

---

noun

diagonals plural

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

---

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.

---

1. A diagonal line segment.

Other Word Forms

Derived Forms

• nondiagonal
  adjective
• diagonally
  adverb
• nondiagonally
  adverb

Inflected Forms

Nouns

• diagonals
  plural

Etymology

Origin of diagonal

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

Diagonal lights on wood ceiling panels are perfectly aligned with white lines on the restaurant’s carpet.

From The Wall Street Journal • Mar. 9, 2026

He had planned to ski Y Gulley or Diagonal Gulley from the Cairngorm Plateau.

From BBC • Dec. 14, 2024

Diagonal bracing in walls is necessary so they don’t rack and fold up like dominoes.

From Seattle Times • Sep. 11, 2023

A project from 2016, “There Have Been and Will be Many San Franciscos,” is an artist book published by Diagonal Press that tackles the shifting, slippery transformation of Auerbach’s beloved hometown.

From New York Times • Jan. 27, 2022

Diagonal from it, the horn of a talking-machine, in shape a large, a violent, a tin morning-glory, was directed full against the company.

From Humoresque A Laugh on Life with a Tear Behind It by Hurst, Fannie

Related Words

• crosswise
• oblique
• slanted