cornerstone
noun [ C ] uk/ˈkɔː.nə.stəʊn/ us/ˈkɔːr.nɚ.stoʊn/
基石;（尤指）奠基石
a stone in a corner of a building, especially one with the date when the building was made or other writing on it
基础，根本
something of great importance that everything else depends on
In most countries, the family unit is still the cornerstone of society. 在大多数国家，家庭仍然是社会的基础单位。