diagonal (diagonals plural )
1 adj A diagonal line or movement goes in a sloping direction, for example, from one corner of a square across to the opposite corner.
usu ADJ n
...a pattern of diagonal lines.
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diagonally adv ADV with v, oft ADV prep
Vaulting the stile, he headed diagonally across the paddock...
2 n-count A diagonal is a line that goes in a sloping direction.
The bed linen is patterned in stylish checks, stripes, diagonals and triangles.
3 n-count In geometry, a diagonal is a straight line that joins two opposite corners in a flat four-sided shape such as a square.
Mark five points an equal distance apart along the diagonals.