The basis of something.
A stone laid during the construction of a (usually important) building, the laying of which is usually marked by a ceremony.
A fundamental rule or principle.
The principle that one should treat other people in the manner in which one would want to be treated by them.
A method of statutory interpretation, whereby a judge will deviate from a literal interpretation of the law to the extent necessary to circumvent obvious absurdities or (sometimes) conclusions repugnant to public policy.