名詞 cornerstone:

1. the fundamental assumptions from which something is begun or developed or calculated or explained
   同義詞：basis, base, foundation, fundament, groundwork
2. a stone in the exterior of a large and important building; usually carved with a date and laid with appropriate ceremonies
3. a stone at the outer corner of two intersecting masonry walls

cornerstone 也作 corner stone

n.（名詞）

A stone at the corner of a building uniting two intersecting walls; a quoin.
墻角石：用于聯(lián)結(jié)一個建筑中兩個相交的墻壁的角落處的石頭；角石
Such a stone, often inscribed, laid at a ceremony marking the origin of a building.
奠基石：在建筑物動工的儀式上設(shè)置的一種銘刻有字的石頭
An indispensable and fundamental basis:
不可分割且根本性的基礎(chǔ)：
例句：
the cornerstone of an argument.
爭論的基礎(chǔ)