Pizza slice borders, e.g

• Halves of diameters
• Circle lines
• Hub-to-rim lines
• Pie-chart features
• Spokes of a wheel, essentially
• Sector's sides
• Half-diameters
• They start in the middle
• Bicycle wheel spokes, e.g

The Collaborative International Dictionary Word definitions in The Collaborative International Dictionary
Radii \Ra"di*i\ (r[=a]"d[i^]*[imac]), n., pl. of Radius .