Main entry: cornerstone
Definition: a stone at the outer corner of two intersecting masonry walls
Main entry: cornerstone
Definition: a stone in the exterior of a large and important building; usually carved with a date and laid with appropriate ceremonies
Main entry: foundation, fundament, groundwork, cornerstone, base, basis
Definition: the fundamental assumptions from which something is begun or developed or calculated or explained
Usage: the whole argument rested on a basis of conjecture