Circle spokes (5)
I believe the answer is:
radii
'circle spokes' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for radii that I've seen before include "Centre-circumference lines" , "Halves of diameters" , "Straight lines from the centre to the surface of a sphere" , "Lines from centre to perimeter of a circle" , "Halves of diameter" .)