Cornerstone

In general:

Cornerstone stands for strength and safety, which may relate to the personality or to plans and goals that will be brought to a successful conclusion.

* Please, see meaning of corner.

Explanation & Definition:

Short explanation
A ceremonial stone set at the corner of a building, joining two exterior walls, and often inscribed with the starting and completion dates of construction, the name of the architect and owner, and other details.

Complete definition
The cornerstone (or foundation stone) concept is derived from the first stone set in the construction of a masonry foundation, important since all other stones will be set in reference to this stone, thus determining the position of the entire structure.

Synonyms of cornerstone
noun: headstone, keystone; plural: headstones, keystones; related terms: fundament, groundwork, basis, foundation, base
explanation, meat and potatoes, supposal, supposition, assumption.