From Longman Dictionary of Contemporary Englishcornerstonecor‧ner‧stone /ˈkɔːnəstəʊn $ ˈkɔːrnərstoʊn/ noun [countable]  1 BASICsomething that is extremely important because everything else depends on itcornerstone of The magazine became the cornerstone of McFadden’s publishing empire.► see thesaurus at  basis2 TBBa stone at one of the bottom corners of a building, often put in place at a special ceremony SYN foundation stone
                                                    
                                                Examples from the Corpus
cornerstone• As a cornerstone, Galvin established the character and culture of the company he wished Motorola to be.• Whatever his manias, his music remains a cornerstone of the classical repertoire.• Local authority direct labour organisations are the cornerstones of training in construction.• All the eulogies he offered seemed to be for the men who had been the cornerstones of the neighborhood.• The theory of plate tectonics explains these phenomena and is commonly regarded as one of the cornerstones of modern geophysics.• In the past, one of the cornerstones of the economic argument for conservation was its value to tourism.• Perhaps an alliance with the East Angles was the cornerstone of Aethelbald's ascendancy.• The Liturgy for that Sunday was the cornerstone of both prayer and reflection.cornerstone of• The magazine became the cornerstone of MacFadden's publishing empire. 
