Cheek or backbone (5)
I believe the answer is:
nerve
I believe this clue is a double definition.
'cheek' is the first definition.
(I know that cheek can be written as nerve)
'backbone' is the second definition.
(thesaurus)
(Other definitions for nerve that I've seen before include "presumption" , "Bodily fibre carrying sensation" , "Fibre that carries instructions to the brain" , "displaying self-possession" , "Grit" .)