Foundation
Cornerstone
noun
The kanji and the word are exactly the same. That means they share meanings as well.
A foundation is made of stone (いし). And it holds up an entire zoo A (ずえ) but none of Zoo B. Zoo B will fall apart when an earthquake hits.
ここにいる人は皆、総合格闘技の礎を築いた故人の死を悼んでいると思います。
I think everyone here is mourning over the deceased who laid the foundation of mixed martial art.
手塚治虫は日本文化の礎となった人物と考えていいと思います。
I think it is safe to say that Osamu Tezuka is a cornerstone of Japanese culture.
大変だ。お城の礎となる石が誰かに壊されてしまった。一刻も早く避難しないと城が崩れるぞ！
Oh, no. Someone broke the stone that forms the foundation of the castle. If we don't evacuate as quickly as possible, the castle will collapse!