1. A stone at the outer corner of two intersecting masonry walls
   "The cornerstone of the historic building bore the date of its construction"
    
2. A stone in the exterior of a large and important building; usually carved with a date and laid with appropriate ceremonies
   "The university president placed a time capsule behind the cornerstone during the groundbreaking ceremony"
    
3. The fundamental assumptions from which something is begun, developed, calculated or explained
   "the whole argument rested on a cornerstone of conjecture";
   - basis, base, foundation, fundament, groundwork

Derived forms: cornerstones

Type of: assumption, stone, supposal, supposition

Part of: building, edifice, explanation

Encyclopedia: Cornerstone, Pennsylvania