foundation stone

Translations
краеугольный камень
Trust is the foundation stone of any relationship.
Доверие - это краеугольный камень любых отношений.
Definitions
A foundation stone is a ceremonial stone set in the foundation of a building, often inscribed with the date of construction and other significant information. It symbolizes the beginning of a construction project and can also represent the fundamental principles or ideas upon which something is built.
Words
foundation

noun
основание
stone

noun
камень