pedra angular angolul

cornerstone [cornerstones]▼(ceremonial stone)
noun
[UK: ˈkɔː.nə.stəʊn] [US: ˈkɔːr.nərˌstoʊn]

keystone [keystones]▼(the top stone of an arch)
noun
[UK: ˈkiː.stəʊn] [US: ˈkiːˌstoʊn]