semiangle
/ˈsɛmiˌæŋɡəl/
noun
- Half of an angle; often used in geometry and optics to describe the angle between the axis and the edge of a cone of light or a field of view.
- The camera lens has a semiangle of 45 degrees, giving a wide field of view.
- In the diagram, the semiangle of the cone is 30 degrees.
- The semiangle of the flashlight's beam determines how wide the light spreads.