Possible Clues:

• Part of build-up of arms, some distance from centre
• Line from the center to the perimeter of a circle
• Centre-circumference length
• Line from the centre to the perimeter of a circle
• Line segment
• Spoke about Darius
• Mountaineer's final farewells, leaving European range
• What r can mean, in geometry
• Wheel spoke, essentially
• Bone that always has one end in the centre