Definition of diagonal
(Entry 1 of 2)
1a
: joining two vertices of a rectilinear figure that are nonadjacent or two vertices of a polyhedral figure that are not in the same face
b
: passing through two nonadjacent edges of a polyhedron
a diagonal plane
2a
: inclined obliquely from a reference line (such as the vertical)
wood with a diagonal grain
b
: having diagonal markings or parts
a diagonal weave
diagonal
nounDefinition of diagonal (Entry 2 of 2)
1
: a diagonal straight line or plane
2a(1)
: a diagonal direction
(2)
: a diagonal row, arrangement, or pattern
b
: something oriented in diagonal position
3
: slash sense 4
on the diagonal
: in an oblique direction : diagonally
Keep scrolling for more
Keep scrolling for more
Keep scrolling for more
Keep scrolling for more
Test Your Vocabulary
Name that Thing: Flower Edition
-
- Name that flower

Test your visual vocabulary with our 10-question challenge!
TAKE THE QUIZ
Spell words. Make bears.
TAKE THE QUIZLove words? Need even more definitions?
Merriam-Webster unabridged
Words at Play
Ask the Editors
Share diagonal
Time Traveler for diagonal
The first known use of diagonal was in 1563
See more words from the same year