Quoin (architecture)
A cornerstone or hardpan is (especially dry and masonry ) built of natural stone masonry in the wall corners.
In addition to a creative cornerstones have a supporting function. They stabilize by their greater weight natural stone walls.
Figurative meaning
In the Bible the word cornerstone is used in a figurative sense.
In Psalm 118, the saving power of God is seen as the cornerstone - laying:
I thank thee that thou hast heard me; you have become my salvation. The stone rejected by the builders has become the cornerstone.
In the New Testament this Psalm shall be headed by Jesus quotes ( (Mt 21,42 EU), Mk 12:10 and Lk 20:17) and referred to him: ( 1 Pt 2 EU).