- (
architecture )建筑 the central stone at the top of an arch that keeps all the other stones in position 拱顶石 Topics Buildingsc2 - [usually singular]
the most important part of a plan or argument that the other parts depend on (计划、论据的)主旨,基础 Changes to the welfare system are the keystone of the government’s reforms. 福利制度的改革是政府改革的重点。