/ ˈbækbəʊn; NAmE -boʊn/ noun
1.
[ C ] the row of small bones that are connected together down the middle of the back
SYN spine —picture at skeleton
2.
[ sing. ] the most important part of a system, an organization, etc. that gives it support and strength :
Agriculture forms the backbone of the rural economy.
3.
[ U ] the strength of character that you need to do sth difficult :
He doesn't have the backbone to face the truth.