1 spine, spinal column:
He's much better since the surgery on his backbone.
2 mainstay, chief or main support, buttress, pillar:
Sheila has been the backbone of the society, but she has now moved away.
3 resoluteness, sturdiness, firmness, determination, strength (of character), mettle, purposefulness, resolution, courage, fortitude, resolve, will, will-power, strength, stability, stamina, staying power, grit:
Has she the backbone to run the company alone?