1. anchor, backbone, keystone, linchpin, lynchpin, mainstay

a central cohesive source of support and stability

Example Sentences:
'faith is his anchor'
'the keystone of campaign reform was the ban on soft money'
'he is the linchpin of this firm'

• anchor
• keystone
• linchpin
• lynchpin
• mainstay

2. backbone, grit, gumption, guts, moxie, sand

fortitude and determination

Example Sentences:
'he didn't have the guts to try it'

• grit
• gumption
• guts
• moxie
• sand

3. back, backbone, rachis, spinal column, spine, vertebral column

the series of vertebrae forming the axis of the skeleton and protecting the spinal cord

Example Sentences:
'the fall broke his back'

• back
• rachis
• spinal column
• spine
• vertebral column

4. backbone, spine

the part of a book's cover that encloses the inner side of the book's pages and that faces outward when the book is shelved

Example Sentences:
'the title and author were printed on the spine of the book'

• spine

5. backbone

the part of a network that connects other networks together

Example Sentences:
'the backbone is the part of a communication network that carries the heaviest traffic'