Meaning & use
diagonal
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Meanings
adjectivecomparable
Going in a slanting straight line, neither horizontal nor vertical, such as from one corner of a square to the opposite one.
Grammar: Normally used before a noun and not usually graded: a diagonal line, a diagonal path.
Patterns
- a diagonal line
- diagonal to something
She drew a diagonal line from the top left of the page to the bottom right.
The shirt has thin diagonal stripes.
A diagonal path crosses the park from gate to gate.
nouncountablemathematics
A straight line joining two corners of a shape that are not next to each other, or any slanting line.
Grammar: Often used in geometry: the diagonal of a rectangle, or cut something on the diagonal.
Patterns
- the diagonal of something
- on the diagonal
Each diagonal of a square divides it into two triangles.
The carpenter cut the board along the diagonal.
In the grid, the bishop can move along any diagonal.
Word forms
| plural | diagonals |
|---|
Common combinations
- diagonal line
- Draw a diagonal line across the paper.
- diagonal stripes
- The flag has bold diagonal stripes in red and white.
- cut on the diagonal
- Cut the sandwich on the diagonal for a neater look.
- cross diagonally
- We crossed the plaza diagonally to save time.
- main diagonal
- In a matrix, the main diagonal runs from top left to bottom right.
Synonyms and how they differ
- slanting
- Slanting describes any tilt away from straight up, while diagonal suggests a definite straight line across a space.
- oblique
- Oblique is more formal and technical, and it covers any angle that is not a right angle.
- sloping
- Sloping is used for surfaces that go up or down, such as a roof, rather than a line across a shape.
- slanted
- Slanted is the everyday word for a tilted surface or line, and it lacks the precise geometric feeling of diagonal.
Opposites
Word family
- diagonally adverb
- in a slanting direction
- diagonalize verb
- a mathematical term meaning to turn a matrix into diagonal form
- diagonalization noun
- the process of diagonalizing a matrix
Commonly confused: diagonal or perpendicular? diagonal or diameter?
diagonal vs perpendicular
Perpendicular means meeting another line at exactly a right angle, which is a different relationship from running diagonally.
diagonal vs diameter
A diameter is a straight line through the center of a circle, while a diagonal belongs to a shape with corners.
Practice
What is a diagonal of a rectangle?
Choose one answer.
A diagonal joins two corners that are not next to each other. Lines along the sides are simply edges, not diagonals.
Make it your own
Write a sentence using “diagonal”, then check it and compare it with the examples above.