Bowels and backbone or nerve (4)
I believe the answer is:
guts
This clue is a triple definition!
'bowels' is the first definition.
('gut' can be a synonym of 'bowel')
'and' acts as a link.
'backbone' is the second definition.
(synonyms)
'or' acts as a link.
'nerve' is the third definition.
(I've seen this in another clue)
(Other definitions for guts that I've seen before include "stamina!" , "Intestinal courage?" , "Intestines; bravery" , "backbone" , "Belly; courage" .)