diagonal
adj.adj. joining two opposite corners of a square or rectangle with a straight, sloping line. You use this to describe something that is slanted rather than straight across or straight up.
adj. joining two non-adjacent vertices of a polygon or two non-adjacent vertices of a polyhedron. Often describes a line or movement that is slanted or oblique relative to a horizontal or vertical axis.
The shirt has a pattern of thin diagonal stripes.
To save time, the hikers took a diagonal path across the field instead of following the perimeter fence.
The architect used diagonal bracing to reinforce the structure against lateral wind forces while maintaining the building's aesthetic profile.
From Middle French diagonal, from Latin diagōnālis, from Ancient Greek διαγώνιος (diagṓnios, “from angle to angle”), from διά (diá, “across”) + γωνία (gōnía, “angle”).
Typically used attributively before a noun; can also function as a noun when referring to the line itself.