cornerstone
US /ˈkɔːr.nɚ.stoʊn/
UK /ˈkɔːr.nɚ.stoʊn/
1.
an important quality or feature on which a particular thing depends or is based
:
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Trust is the cornerstone of any strong relationship.
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Education is the cornerstone of a prosperous society.
2.
a stone that forms the base of a corner of a building, especially one laid at a formal ceremony
:
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The mayor laid the cornerstone for the new library.
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The date of construction was carved into the cornerstone.