Bone that is broken in accident initially (5)
I believe the answer is:
tibia
'bone' is the definition.
(I know that tibia is a type of leg bone)
'that is broken in accident initially' is the wordplay.
'initially' suggests taking the first letters.
The initial letters of 'that is broken in accident' is 'TIBIA'.
(Other definitions for tibia that I've seen before include "part of skeleton" , "The formal shinbone" , "Bone in osso bucco" , "Bone of the lower leg" , "ancient pipe" .)