#cornerstone  a stone at the outer corner of two intersecting masonry walls
  supertype:  stone  building material consisting of a piece of rock hewn in a definite shape for a special purpose; "he wanted a special stone to mark the site"
  part of:  edifice__building  a structure that has a roof and walls and stands more or less permanently in one place; "there was a three-story building on the corner"; "it was an imposing edifice"

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