土ど台だい石いし

noun

cornerstone; foundation stone

Refers to a stone used as the base or cornerstone of a building, both literally and figuratively.

• この建たて物ものの土ど台だい石いしは江え戸ど時じ代だいから使つかわれている。

  The foundation stones of this building have been used since the Edo period.

• 教きょう育いくは社しゃ会かいの土ど台だい石いしだ。

  Education is the cornerstone of society.