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

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

• 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; 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

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

From Seattle Times • Sep. 11, 2023

Through the side project Diagonal Press, Auerbach publishes open-edition artist books and specimen posters of the typefaces they design in their spare time.

From New York Times • Mar. 16, 2023

The $12 million Crossing at Auld Farms off Diagonal Road will offer 51 single-family detached homes in West Akron.

From Washington Times • Mar. 29, 2021

Diagonal lines of thread are first laid from edge to edge of the ground space, and these are sewn down by short overcasting stitches in the cross direction.

From Art in Needlework A Book about Embroidery by Buckle, Mary

Related Words

• crosswise
• oblique
• slanted