backbone
n. countable B2 Upper Intermediate US //ˈbækˌboʊn// UK //bˈækbəʊn// back·bone
n. the main source of strength or support for something. You use this to describe the most important part of a plan, organization, or system.
n. the central element that provides structural support or stability to a system, organization, or argument. Metaphorical usage is common in general discourse.
Trust is the backbone of our friendship.
Small businesses form the backbone of the local economy.
The committee's rigorous data analysis served as the backbone of the final report, ensuring that every recommendation was grounded in empirical evidence rather than speculation.
From Middle English bakbon, bakebon, bac-bon; equivalent to back + bone. Compare the semantically analogous English ridgebone.