[ dahy-ag-uh-nl, -ag-nl ]
See synonyms for: diagonaldiagonalsdiagonally on Thesaurus.com

  1. Mathematics.

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

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

  2. having an oblique direction.

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

  1. a diagonal line or plane.

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

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

  3. 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 ).

  4. Chess. one of the oblique lines of squares on a chessboard: He advanced his bishop along the open diagonal.

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, -al1

Other words from diagonal

  • di·ag·o·nal·ly, adverb
  • non·di·ag·o·nal, adjective, noun
  • non·di·ag·o·nal·ly, adverb

Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2023

How to use diagonal in a sentence

British Dictionary definitions for diagonal


/ (daɪˈæɡənəl) /

  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

  1. marked with slanting lines or patterns

  1. maths a diagonal line or plane

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

  1. cloth marked or woven with slanting lines or patterns

  2. something put, set, or drawn obliquely

  3. another name for solidus (def. 1)

  4. 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

Origin of diagonal

C16: from Latin diagōnālis, from Greek diagōnios, from dia- + gōnia angle

Derived forms of diagonal

  • diagonally, adverb

Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Scientific definitions for diagonal


[ dī-ăgə-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.

The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.