Subtend/səbˈtend/ Definition 1 of 2Pro Tip 1/3Geometry Usage Used to describe how an angle relates to a shape in geometry, like an arc or line. In this triangle, the top angle subtends the base. Pro Tip 2/3Visual Imagery Imagine drawing lines from the angle's vertex to the endpoints of the arc or side it faces. This angle subtends a larger arc than that one. Pro Tip 3/3More Than Angles Though commonly associated with angles, other shapes can subtend parts of geometric figures. The diameter of the circle subtends a semicircle.