More than one spoke of bones in the arm (5)
I believe the answer is:
radii
This clue could be a double definition.
'more than one spoke' is the first definition.
(I've seen this before)
'bones in the arm' is the second definition.
'radii' can be an answer for 'bones' (radius is a kind of bone). I'm not sure about the 'in the arm' bit.
'of' is the link.
Can you help me to learn more?
(Other definitions for radii that I've seen before include "Lines from centre to perimeter of a circle" , "spoke several times" , "spoke with others" , "more than one spoke" , "Spokes of wheel - bones of arm" .)