corner-stone

Noun

cornerstone (plural cornerstones)

1. A stone forming the base at the corner of a building.
   • Clutch it like a cornerstone
     Otherwise it all comes down
     Justify denials and
     Grip 'em to the lonesome end2001, Tool, “The Grudge”, in Lateralus (progressive metal, alternative metal)
2. Such a stone used ceremonially, often inscribed with the architect's and owner's names, dates and other details.
   • The cornerstone on the Flatiron Building is set on the Fifth Avenue facade.
3. (figuratively) That which is prominent, fundamental, noteworthy, or central.
   • Exceptional service is the cornerstone of the hospitality industry.