a central stone at the summit of an arch, locking the whole together
拱顶石。
[usu. in sing.]the central principle or part of a policy, system, etc., on which all else depends
基础;主旨;基本原则
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cooperation remains the keystone of the government's security policy .合作仍然是政府安全政策的基本原则。
a US film company formed in 1912, remembered for its silent slapstick comedy films, many featuring the bumbling Keystone Kops police characters
吉斯通电影公司(成立于1912年的美国电影公司,以其无声喜剧电影而为人铭记,其中许多电影描绘的是笨拙的吉斯通式的警察人物)。