Definition of diagonal in English:

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Pronunciation: /dīˈaɡənl/
(abbreviation diag.)


1(Of a straight line) joining two opposite corners of a square, rectangle, or other straight-sided shape.
Example sentences
  • Draw two diagonal lines dividing the square and the rectangle into triangles.
  • One option is to draw a diagonal line between two opposite points to represent movement between here and there.
  • The design was very nice, with diagonal lines forming a grid, each square filled with a snapshot of the movie in rich, warm tones.
1.1(Of a line) straight and at an angle; slanting: a tie with diagonal stripes
More example sentences
  • The film, with the exception of one shot, is composed of precisely two camera angles: a diagonal shot from the dashboard towards the passenger seat, and another, similar shot towards the driver seat.
  • Pencil-thin diagonal blues and greens angle across the surface like tracer-bullet tracks streaking across a movie screen.
  • Score the squid by holding the knife at an angle and making diagonal cuts, taking care not to cut right through.
crosswise, crossways, slanting, slanted, aslant, oblique, angled, at an angle;
cater-cornered, kitty-cornered


1A straight line joining two opposite corners of a square, rectangle, or other straight-sided shape.
Example sentences
  • Do this at a diagonal, from one corner of the square to the opposite corner.
  • For example, the Pythagoreans did not expect to uncover irrational numbers in the diagonal of a square.
  • The particular tablet which concerns us is not one relating to administration but one which presents a geometrical problem which asks for the dimensions of a rectangle whose area and diagonal are known.
1.1 Mathematics The set of elements of a matrix that lie on a line joining two opposite corners.
Example sentences
  • The alpha values and the mean interitem correlations are presented in the diagonals of the matrices in Table 2.
  • The diagonal of the rate matrix is specified such that the row sums are equal to zero.
  • If we restrict ourselves to the 2x2 arrays whose diagonals lie on the main diagonal of the table, then the sum of four numbers in the array is always a perfect square.
1.2A slanting straight pattern or line: the bars of light made diagonals across the entrance tiles can be laid on the diagonal
More example sentences
  • Let stand ten minutes, then slice very thin and on the diagonal.
  • Take cuttings from last seasons growth, cut just below the bud and trim the top on the diagonal.
  • The paintings are thick with diagonals; light is pure color, color is pure stroke.
1.3 Chess A slanting row of squares whose color is the same.
Example sentences
  • If you move a pawn to open up a diagonal for a bishop, then should you usually NOT move up another pawn to develop the bishop on the other diagonal.
  • After a queen pawn opening, Hort threatened mate on the long diagonal.
  • As frequently happens in such a situation, White does not have a diagonal for his dark Bishop, nor does he have any other diagonals from which to aim at his opponent's King.


Mid 16th century: from Latin diagonalis, from Greek diagōnios 'from angle to angle', from dia 'through' + gōnia 'angle'.

  • pentagon from late 16th century:

    The Greek expertise in geometry means that many geometrical forms have Greek names. The five-sided pentagon is formed from penta ‘five’ and gonia ‘angle’, just as polygon (late 16th century) is formed from the word for ‘many’ plus -gon and diagonal (mid 16th century) with dia ‘through’. Penta is also found in words such as the mystic figures of the pentangle (Late Middle English), pentacle (late 16th century), and pentagram (mid 19th century), and in the pentathlon (early 17th century), once the original five events of leaping, running, discus-throwing, spear-throwing, and wrestling of ancient Greek and Roman games. Fifty is found in Pentecost (Old English) which came via ecclesiastical Latin from Greek pentēkostē (hēmera) ‘fiftieth (day)’. The Jewish festival of Shavuoth is held on the fiftieth day after the second day of Passover. The Christian festival is held on the seventh Sunday after Easter commemorating the descent of the Holy Spirit on the disciples as recorded in Acts 2.

Words that rhyme with diagonal

heptagonal, hexagonal, octagonal, tetragonal

For editors and proofreaders

Syllabification: di·ag·o·nal

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