cornerstone

A cornerstone is a very important part of a building that holds everything together.

When we think about cornerstones, we often imagine a big stone at the foundation of a house or a wall. But the word has a broader meaning too - it can also describe something that's crucial to an idea, a project, or even a community. For example, a new law might be considered the cornerstone of a country's justice system because it sets the tone for how people are treated and punished. In this sense, a cornerstone is like a foundation stone - it provides stability and direction for everything else that follows.