An oblique line is a line that is not horizontal or vertical. It is slanted at an angle. There are many synonyms for the word "oblique line," including slanting line, diagonal line, tilted line, skewed line, and inclined line. Each of these words describes a line that is not perfectly straight up and down or side to side. Oblique lines are used in art, design, and architecture to create dynamic compositions and add interest to otherwise static shapes. They can also be used in mathematics and geometry to describe the slope of a line or the angle between two lines.