back·bone 
/ˈbækˌboʊn/ noun
plural back·bones /ˈbækˌboʊn/ noun 1 [count] : the row of connected bones that go down the middle of the back and protect the spinal cord —called also spinal column, spine; — see picture at human 2 [count] : the most important or strongest part of something
▪ She is the backbone of the family. 3 [noncount] : strength and courage
▪ He showed some backbone by refusing to compromise his values.
▪ She is the backbone of the family.
▪ He showed some backbone by refusing to compromise his values.
